Apply suggestion from @Copilot

Co-authored-by: Copilot <[email protected]>
Signed-off-by: Mark Kurtz <[email protected]>

Author: markurtz

src/guidellm/utils/messaging.py

@@ -426,7 +426,7 @@ async def stop(self):
         await super().stop()
         self.send_queue.close()
         self.done_queue.close()
-        self.buffer_send_queue = None
+        self.send_queue = None
         self.done_queue = None
 
     async def receive_messages_task(