Pop metadata key in test

tests/unit/server/api/test_subscriptions.py

@@ -1207,6 +1207,7 @@ async def test_emits_expected_payloads_and_records_expected_spans_and_experiment
         assert isinstance(experiment_description := experiment.pop("description"), str)
         assert "dataset-name" in experiment_description
         assert experiment.pop("projectName") == "playground"
+        assert experiment.pop("metadata") == {}
         assert isinstance(created_at := experiment.pop("createdAt"), str)
         assert isinstance(updated_at := experiment.pop("updatedAt"), str)
         assert created_at == updated_at