Fix: Correct parameter retrieval in thumbup api (#6114)

### What problem does this PR solve?

https://github.com/infiniflow/ragflow/issues/5546

up_down was using req.get("set") to retrieve the parameter, but
according to the frontend code, it should be req.get("thumbup").



![image](https://github.com/user-attachments/assets/7189c982-f80e-48c9-a0a3-40f8a5d9e47b)



1842ca0334/web/src/interfaces/request/chat.ts (L3)


1842ca0334/api/apps/conversation_app.py (L327)

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

Co-authored-by: zhaozhicheng <zhicheng.zhao@fastonetech.com>

api/apps/conversation_app.py

@@ -324,7 +324,7 @@ def thumbup():
     e, conv = ConversationService.get_by_id(req["conversation_id"])
     if not e:
         return get_data_error_result(message="Conversation not found!")
-    up_down = req.get("set")
+    up_down = req.get("thumbup")
     feedback = req.get("feedback", "")
     conv = conv.to_dict()
     for i, msg in enumerate(conv["message"]):