diff --git a/.gitlab-ci/pipeline.yml b/.gitlab-ci/pipeline.yml
index aee319106be0bf4e0008802ac812af0d7bc6e743..3c45b444356eeb54f0dfc39149c9a5fcc24383d4 100644
--- a/.gitlab-ci/pipeline.yml
+++ b/.gitlab-ci/pipeline.yml
@@ -204,7 +204,8 @@ variables:
     - <<: *with-database
   variables:
     TESTSUITE: PHPUnit-Unit
-    KUBERNETES_CPU_REQUEST: "16"
+    KUBERNETES_CPU_REQUEST: "1"
+    CONCURRENCY: 6
 
 '✅️ PHPStan Tests':
   <<: [ *default-job-settings ]
diff --git a/core/modules/phpass/tests/src/Unit/PasswordVerifyTest.php b/core/modules/phpass/tests/src/Unit/PasswordVerifyTest.php
index dd897c00a0fdb7347adfda7c369232cdfcc90087..f32cb022447f44d0c2f0fb6c73facf21c0b8b17e 100644
--- a/core/modules/phpass/tests/src/Unit/PasswordVerifyTest.php
+++ b/core/modules/phpass/tests/src/Unit/PasswordVerifyTest.php
@@ -14,6 +14,7 @@
  *
  * @coversDefaultClass \Drupal\phpass\Password\PhpassHashedPassword
  * @group phpass
+ * @group #slow
  */
 class PasswordVerifyTest extends UnitTestCase {
 
diff --git a/core/phpcs.xml.dist b/core/phpcs.xml.dist
index 54bdfe45052a961b005fb839f569bccf92fa0d66..8467644b0479e1eedde5ece3789b3a7f0720a089 100644
--- a/core/phpcs.xml.dist
+++ b/core/phpcs.xml.dist
@@ -8,8 +8,9 @@
   <exclude-pattern>*/node_modules/*</exclude-pattern>
   <!--Exclude third party code.-->
   <exclude-pattern>./assets/vendor/*</exclude-pattern>
-  <!--Exclude the PHPStan baseline from coding standards.-->
+  <!--Exclude the PHPStan baseline and temp dir from coding standards.-->
   <exclude-pattern>./core/.phpstan-baseline.php</exclude-pattern>
+  <exclude-pattern>./core/phpstan-tmp/*</exclude-pattern>
   <!-- Exclude third-party code maintained within core that does not follow our standards. -->
   <!-- @todo This rule may be removed when https://www.drupal.org/node/1848264 is resolved. -->
   <exclude-pattern>./core/lib/Drupal/Component/Diff/</exclude-pattern>
diff --git a/core/tests/Drupal/Tests/Component/Datetime/TimeWithNoRequestTest.php b/core/tests/Drupal/Tests/Component/Datetime/TimeWithNoRequestTest.php
index 69bac3cb0282fbcfda2d426a928b14c081f9826d..d4b02de5d30a0a9ac938a038708d348020922d80 100644
--- a/core/tests/Drupal/Tests/Component/Datetime/TimeWithNoRequestTest.php
+++ b/core/tests/Drupal/Tests/Component/Datetime/TimeWithNoRequestTest.php
@@ -12,6 +12,7 @@
  *
  * @coversDefaultClass \Drupal\Component\Datetime\Time
  * @group Datetime
+ * @group #slow
  * @runTestsInSeparateProcesses
  * @preserveGlobalState disabled
  */
diff --git a/core/tests/Drupal/Tests/Component/Utility/RectangleTest.php b/core/tests/Drupal/Tests/Component/Utility/RectangleTest.php
index f7a77f6e7db5a9e16f72b17030d81156b6307683..c43054055fbcac97572daea35c3e865534b51c6b 100644
--- a/core/tests/Drupal/Tests/Component/Utility/RectangleTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/RectangleTest.php
@@ -10,6 +10,7 @@
 /**
  * @coversDefaultClass \Drupal\Component\Utility\Rectangle
  * @group Image
+ * @group #slow
  */
 class RectangleTest extends TestCase {
 
diff --git a/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
index 0cc920d5f0dafa688904408928f3b89efe250957..f2fd94290332a26fdb9d9e5e64d7b04e8be14c53 100644
--- a/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
@@ -9,6 +9,7 @@
 
 /**
  * @group Utility
+ * @group #slow
  *
  * @coversDefaultClass \Drupal\Component\Utility\UrlHelper
  */
diff --git a/core/tests/Drupal/Tests/Component/Utility/XssTest.php b/core/tests/Drupal/Tests/Component/Utility/XssTest.php
index 15b1f0384342d0371d82d4a940b40c0ea64c232b..6f8e09425b02bd937a9704b342e8b7bf0b98e8a7 100644
--- a/core/tests/Drupal/Tests/Component/Utility/XssTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/XssTest.php
@@ -23,6 +23,7 @@
  *   CVE-2006-1226 (= rev. 1.112?), CVE-2008-0273, CVE-2008-3740.
  *
  * @group Utility
+ * @group #slow
  * @coversDefaultClass \Drupal\Component\Utility\Xss
  * @runTestsInSeparateProcesses
  */
diff --git a/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ComposerHookTest.php b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ComposerHookTest.php
index 7c7a10909c1b8036325005a35dd042641d9b2bed..14d896ad182388c798d8bf003b3f83589029e6c4 100644
--- a/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ComposerHookTest.php
+++ b/core/tests/Drupal/Tests/Composer/Plugin/Scaffold/Functional/ComposerHookTest.php
@@ -23,6 +23,7 @@
  * information.
  *
  * @group Scaffold
+ * @group #slow
  */
 class ComposerHookTest extends BuildTestBase {
 
diff --git a/core/tests/Drupal/Tests/Core/Command/QuickStartTest.php b/core/tests/Drupal/Tests/Core/Command/QuickStartTest.php
index 17c12d2d394e0545b3164a4af951bef1c4c30e7b..07a3740f36a7b419e846bd0a9a98cac07003a50e 100644
--- a/core/tests/Drupal/Tests/Core/Command/QuickStartTest.php
+++ b/core/tests/Drupal/Tests/Core/Command/QuickStartTest.php
@@ -24,6 +24,7 @@
  * @requires extension pdo_sqlite
  *
  * @group Command
+ * @group #slow
  */
 class QuickStartTest extends TestCase {
 
diff --git a/core/tests/Drupal/Tests/Core/DrupalKernel/DrupalKernelTest.php b/core/tests/Drupal/Tests/Core/DrupalKernel/DrupalKernelTest.php
index e01add0147746f34ae011fa5eb0e1025632f6200..845937dee5472cc64d5937dddea134735e03c260 100644
--- a/core/tests/Drupal/Tests/Core/DrupalKernel/DrupalKernelTest.php
+++ b/core/tests/Drupal/Tests/Core/DrupalKernel/DrupalKernelTest.php
@@ -14,6 +14,7 @@
 /**
  * @coversDefaultClass \Drupal\Core\DrupalKernel
  * @group DrupalKernel
+ * @group #slow
  */
 class DrupalKernelTest extends UnitTestCase {
 
diff --git a/core/tests/Drupal/Tests/Core/EventSubscriber/ActiveLinkResponseFilterTest.php b/core/tests/Drupal/Tests/Core/EventSubscriber/ActiveLinkResponseFilterTest.php
index cdd08cfbf431ffc7efcfdbe9e10049ba87102ab0..4c830fecfe5f7bb4e28f5a12a23e82a540e90a39 100644
--- a/core/tests/Drupal/Tests/Core/EventSubscriber/ActiveLinkResponseFilterTest.php
+++ b/core/tests/Drupal/Tests/Core/EventSubscriber/ActiveLinkResponseFilterTest.php
@@ -27,6 +27,7 @@
 /**
  * @coversDefaultClass \Drupal\Core\EventSubscriber\ActiveLinkResponseFilter
  * @group EventSubscriber
+ * @group #slow
  */
 class ActiveLinkResponseFilterTest extends UnitTestCase {
 
diff --git a/core/tests/Drupal/Tests/Core/Recipe/RecipeQuickStartTest.php b/core/tests/Drupal/Tests/Core/Recipe/RecipeQuickStartTest.php
index c71cd91bff0586c64a54ca4e549fc7d45b2b9626..65bedfff3d0daeeace043a1b0d6ad7f61838b74a 100644
--- a/core/tests/Drupal/Tests/Core/Recipe/RecipeQuickStartTest.php
+++ b/core/tests/Drupal/Tests/Core/Recipe/RecipeQuickStartTest.php
@@ -25,6 +25,7 @@
  *
  * @group Command
  * @group Recipe
+ * @group #slow
  */
 class RecipeQuickStartTest extends TestCase {
 
diff --git a/core/tests/Drupal/Tests/Core/Security/RequestSanitizerTest.php b/core/tests/Drupal/Tests/Core/Security/RequestSanitizerTest.php
index ee3394b6391da0463dc24b198ef8a47da0bfa29e..59f17d3e15fa34953a417cb169c5e6d62068e54a 100644
--- a/core/tests/Drupal/Tests/Core/Security/RequestSanitizerTest.php
+++ b/core/tests/Drupal/Tests/Core/Security/RequestSanitizerTest.php
@@ -15,6 +15,7 @@
  * @runTestsInSeparateProcesses
  * @preserveGlobalState disabled
  * @group Security
+ * @group #slow
  */
 class RequestSanitizerTest extends UnitTestCase {
 
diff --git a/core/tests/Drupal/Tests/Core/Site/SettingsTest.php b/core/tests/Drupal/Tests/Core/Site/SettingsTest.php
index d378dcf983c33f63752338a348f14df25f0d0dbe..cb00324bdaf368ce3596a299e3ffbe610ecd9a97 100644
--- a/core/tests/Drupal/Tests/Core/Site/SettingsTest.php
+++ b/core/tests/Drupal/Tests/Core/Site/SettingsTest.php
@@ -14,6 +14,7 @@
  * @coversDefaultClass \Drupal\Core\Site\Settings
  * @runTestsInSeparateProcesses
  * @group Site
+ * @group #slow
  */
 class SettingsTest extends UnitTestCase {
 
diff --git a/core/tests/Drupal/Tests/Core/Test/PhpUnitCliTest.php b/core/tests/Drupal/Tests/Core/Test/PhpUnitCliTest.php
index 5ec76e7820fc61c12d82d852a09d8b5304c67827..bfb3c31e58ee31afa6e0d56bbe89feb75b3dcabf 100644
--- a/core/tests/Drupal/Tests/Core/Test/PhpUnitCliTest.php
+++ b/core/tests/Drupal/Tests/Core/Test/PhpUnitCliTest.php
@@ -10,6 +10,7 @@
 /**
  * @group TestSuites
  * @group Test
+ * @group #slow
  */
 class PhpUnitCliTest extends UnitTestCase {
 
diff --git a/core/tests/Drupal/Tests/Core/Update/UpdateRegistryTest.php b/core/tests/Drupal/Tests/Core/Update/UpdateRegistryTest.php
index d183cd752d175586e3fe3ff726870513ab994315..9c8f72087e165278f2fe811f60ab8e80a70b4d25 100644
--- a/core/tests/Drupal/Tests/Core/Update/UpdateRegistryTest.php
+++ b/core/tests/Drupal/Tests/Core/Update/UpdateRegistryTest.php
@@ -19,6 +19,7 @@
  *
  * @coversDefaultClass \Drupal\Core\Update\UpdateRegistry
  * @group Update
+ * @group #slow
  * @runTestsInSeparateProcesses
  * @preserveGlobalState disabled
  */
diff --git a/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php b/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php
index 893a55e93092aa1328c960b9543504c09d1172c9..a5e71bfb4d8ccbdb1bf801257ff7fb686263f05b 100644
--- a/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php
+++ b/core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php
@@ -26,6 +26,7 @@
  * @see \Drupal\TestSite\Commands\TestSiteTearDownCommand
  *
  * @group Setup
+ * @group #slow
  * @runTestsInSeparateProcesses
  * @preserveGlobalState disabled
  */