fix mypy

Author: habema

examples/realtime/app/server.py

@@ -4,11 +4,12 @@
 import logging
 import struct
 from contextlib import asynccontextmanager
-from typing import TYPE_CHECKING, Any, assert_never
+from typing import TYPE_CHECKING, Any
 
 from fastapi import FastAPI, WebSocket, WebSocketDisconnect
 from fastapi.responses import FileResponse
 from fastapi.staticfiles import StaticFiles
+from typing_extensions import assert_never
 
 from agents.realtime import RealtimeRunner, RealtimeSession, RealtimeSessionEvent