Realtime: fix typecheck error (#1558)

Author: rm-openai

src/agents/realtime/openai_realtime.py

@@ -148,7 +148,7 @@ class _InputAudioBufferTimeoutTriggeredEvent(BaseModel):
 ServerEventTypeAdapter: TypeAdapter[AllRealtimeServerEvents] | None = None
 
 
-def get_server_event_type_adapter():
+def get_server_event_type_adapter() -> TypeAdapter[AllRealtimeServerEvents]:
     global ServerEventTypeAdapter
     if not ServerEventTypeAdapter:
         ServerEventTypeAdapter = TypeAdapter(AllRealtimeServerEvents)
@@ -490,7 +490,7 @@ async def _handle_ws_event(self, event: dict[str, Any]):
         try:
             if "previous_item_id" in event and event["previous_item_id"] is None:
                 event["previous_item_id"] = ""  # TODO (rm) remove
-            parsed: OpenAIRealtimeServerEvent = self._server_event_type_adapter.validate_python(
+            parsed: AllRealtimeServerEvents = self._server_event_type_adapter.validate_python(
                 event
             )
         except pydantic.ValidationError as e: