#3274419 Makes BaseFieldOverride inherit the internal property from the base field.

Closes #3274419

core/modules/mysql/tests/src/Unit/ConnectionTest.php

 <?php
 
-namespace Drupal\Tests\Core\Database\Driver\mysql;
+namespace Drupal\Tests\mysql\Unit;
 
 use Drupal\mysql\Driver\Database\mysql\Connection;
 use Drupal\Tests\UnitTestCase;