Fix shutdown middleware hook (#357)

Co-authored-by: Pavel Kirilin <win10@list.ru>

Author: hawang-wish

taskiq/abc/broker.py

@@ -215,7 +215,7 @@ async def shutdown(self) -> None:
 
         for middleware in self.middlewares:
             if middleware.__class__.shutdown != TaskiqMiddleware.shutdown:
-                await maybe_awaitable(middleware.shutdown)
+                await maybe_awaitable(middleware.shutdown())
 
         await self.result_backend.shutdown()