Issue #3186999 by alexpott, neclimdul, longwave: Make the version a private class property

(cherry picked from commit 702514c1)

core/lib/Drupal/Core/Database/Driver/mysql/Connection.php

@@ -65,6 +65,15 @@ class Connection extends DatabaseConnection {
    */
   protected $needsCleanup = FALSE;
 
+  /**
+   * Stores the server version after it has been retrieved from the database.
+   *
+   * @var string
+   *
+   * @see \Drupal\Core\Database\Driver\mysql\Connection::version
+   */
+  private $serverVersion;
+
   /**
    * The minimal possible value for the max_allowed_packet setting of MySQL.
    *
@@ -290,11 +299,10 @@ protected function getMariaDbVersionMatch(): ?string {
    *   The PDO server version.
    */
   protected function getServerVersion(): string {
-    static $server_version;
-    if (!$server_version) {
-      $server_version = $this->connection->query('SELECT VERSION()')->fetchColumn();
+    if (!$this->serverVersion) {
+      $this->serverVersion = $this->connection->query('SELECT VERSION()')->fetchColumn();
     }
-    return $server_version;
+    return $this->serverVersion;
   }
 
   public function databaseType() {

core/tests/Drupal/Tests/Core/Database/Driver/mysql/ConnectionTest.php

@@ -10,7 +10,6 @@
  *
  * @coversDefaultClass \Drupal\Core\Database\Driver\mysql\Connection
  * @group Database
- * @runTestsInSeparateProcesses
  */
 class ConnectionTest extends UnitTestCase {