Issue #3467391 by catch, smustgrave: Reduce CPU requirement and concurrency for unit tests

.gitlab-ci/pipeline.yml

core/modules/phpass/tests/src/Unit/PasswordVerifyTest.php

...Drupal/Tests/Component/Datetime/TimeWithNoRequestTest.php

core/tests/Drupal/Tests/Component/Utility/RectangleTest.php

core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php

core/tests/Drupal/Tests/Component/Utility/XssTest.php

.../Composer/Plugin/Scaffold/Functional/ComposerHookTest.php

core/tests/Drupal/Tests/Core/Command/QuickStartTest.php

...tests/Drupal/Tests/Core/DrupalKernel/DrupalKernelTest.php

...sts/Core/EventSubscriber/ActiveLinkResponseFilterTest.php

core/tests/Drupal/Tests/Core/Recipe/RecipeQuickStartTest.php

...tests/Drupal/Tests/Core/Security/RequestSanitizerTest.php

core/tests/Drupal/Tests/Core/Site/SettingsTest.php

core/tests/Drupal/Tests/Core/Test/PhpUnitCliTest.php

core/tests/Drupal/Tests/Core/Update/UpdateRegistryTest.php

core/tests/Drupal/Tests/Scripts/TestSiteApplicationTest.php