Fix: rerank issue. (#5696)

### What problem does this PR solve?

#5673

### Type of change

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

rag/llm/rerank_model.py

 #
 import re
 import threading
+from collections.abc import Iterable
 from urllib.parse import urljoin
 
 import requests
         else:
             scores = self._model.compute_score(batch_pairs, max_length=max_length)
         scores = sigmoid(np.array(scores)).tolist()
+        if not isinstance(scores, Iterable):
+            scores = [scores]
         return scores
 
     def similarity(self, query: str, texts: list):