fix: typecheck

Author: giancarloromeo

packages/service-library/src/servicelib/fastapi/app_server.py

@@ -14,7 +14,7 @@
 class FastAPIAppServer(BaseAppServer):
     def __init__(self, app: FastAPI):
         self._app = app
-        self._lifespan_manager = None
+        self._lifespan_manager: LifespanManager | None = None
         self._shutdown_event = asyncio.Event()
 
     @property