Issue #3441577 add property types

Closes #3441577

automatic_updates_extensions/tests/modules/automatic_updates_extensions_test_api/src/ApiController.php

@@ -18,7 +18,7 @@ class ApiController extends PackageManagerApiController {
   /**
    * {@inheritdoc}
    */
-  protected $finishedRoute = 'automatic_updates_extensions_test_api.finish';
+  protected string $finishedRoute = 'automatic_updates_extensions_test_api.finish';
 
   /**
    * {@inheritdoc}