Fix insufficient mocking in test

tests/handlers/test_e2e_keys.py

@@ -891,14 +891,20 @@ def test_query_all_devices_caches_result(self, device_ids: Iterable[str]) -> Non
             new_callable=mock.MagicMock,
             return_value=make_awaitable(["some_room_id"]),
         )
+        mock_get_users = mock.patch.object(
+            self.store,
+            "get_users_server_still_shares_room_with",
+            new_callable=mock.MagicMock,
+            return_value=make_awaitable({remote_user_id}),
+        )
         mock_request = mock.patch.object(
             self.hs.get_federation_client(),
             "query_user_devices",
             new_callable=mock.MagicMock,
             return_value=make_awaitable(response_body),
         )
 
-        with mock_get_rooms, mock_request as mocked_federation_request:
+        with mock_get_rooms, mock_get_users, mock_request as mocked_federation_request:
             # Make the first query and sanity check it succeeds.
             response_1 = self.get_success(
                 e2e_handler.query_devices(