fix: typecheck

Author: giancarloromeo

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

@@ -21,7 +21,9 @@ def __init__(self, app: FastAPI):
 
     @property
     def task_manager(self) -> TaskManager:
-        return self.app.state.task_manager
+        assert self.app.state.task_manager, "Task manager is not initialized"  # nosec
+        task_manager: TaskManager = self.app.state.task_manager
+        return task_manager
 
     async def lifespan(self, startup_completed_event: threading.Event) -> None:
         async with LifespanManager(