Issue #3262284: clean up package_manager_test_validation\TestSubscriber and classes that extend it

tests/modules/automatic_updates_test/src/ReadinessChecker/TestSubscriber1.php

@@ -8,7 +8,7 @@ use Drupal\package_manager_test_validation\TestSubscriber;
 /**
  * A test readiness checker.
  */
-class TestChecker1 extends TestSubscriber {
+class TestSubscriber1 extends TestSubscriber {
 
   /**
    * {@inheritdoc}