test: satisfy propespector

Author: boromir674

tests/e2e/notification/test_composition_listener.py

@@ -63,4 +63,4 @@ def update_with_typo(self, subject): ...
     with pytest.raises(
         TypeError, match="Attached observer .* does not have a callable 'update' method."
     ):
-        _client = ClientObserver()
+        ClientObserver()