Clarify docstring.

tests/handlers/test_e2e_keys.py

@@ -1018,7 +1018,7 @@ def test_query_appservice(self) -> None:
 
     @override_config({"experimental_features": {"msc3984_appservice_key_query": True}})
     def test_query_local_devices_appservice(self) -> None:
-        """If the user has no devices, we expect an empty list."""
+        """Test that querying of appservices for keys overrides responses from the database."""
         local_user = "@boris:" + self.hs.hostname
         device_1 = "abc"
         device_2 = "def"