Fixed import of assert_never from typing

tests/test_lifespan_scoped_dependencies/testing_utilities.py

@@ -1,5 +1,6 @@
 from enum import Enum
-from typing import Any, AsyncGenerator, Generator, TypeVar, Union, assert_never
+from typing import Any, AsyncGenerator, Generator, TypeVar, Union
+from typing_extensions import assert_never
 
 from fastapi import APIRouter, FastAPI, WebSocket
 from starlette.testclient import TestClient