Add exists method to RemoveOldVersionMessageHandlerTest

Introduce the exists method to handle checks for StoredObject or StoredObjectVersion in test cases. This modification ensures consistency and proper exception handling in the testing framework.

src/Bundle/ChillDocStoreBundle/Tests/Service/StoredObjectCleaner/RemoveOldVersionMessageHandlerTest.php

@@ -120,4 +120,9 @@ class DummyStoredObjectManager implements StoredObjectManagerInterface
     {
         throw new \RuntimeException();
     }
+
+    public function exists(StoredObject|StoredObjectVersion $document): bool
+    {
+        throw new \RuntimeException();
+    }
 }