fix: handle coroutine check for on_disconnect callback in chat API (#3930)

Handle coroutine check for on_disconnect callback in chat API

src/backend/base/langflow/api/v1/chat.py

@@ -448,7 +448,9 @@ class DisconnectHandlerStreamingResponse(StreamingResponse):
             message = await receive()
             if message["type"] == "http.disconnect":
                 if self.on_disconnect:
-                    await self.on_disconnect()
+                    coro = self.on_disconnect()
+                    if asyncio.iscoroutine(coro):
+                        await coro
                 break