fix: bug similarity() in YoudaoRerank (#1084)

### What problem does this PR solve?

bix fix

### Type of change

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

rag/llm/rerank_model.py

@@ -125,7 +125,7 @@ class YoudaoRerank(DefaultRerank):
             scores = self._model.compute_score(pairs[i:i + batch_size], max_length=self._model.max_length)
             scores = sigmoid(np.array(scores)).tolist()
             if isinstance(scores, float): res.append(scores)
-            res.extend(scores)
+            else: res.extend(scores)
         return np.array(res), token_count