Fix keys of Xinference deployed models, especially has the same model name with public hosted models. (#2832)

### What problem does this PR solve?

Fix keys of Xinference deployed models, especially has the same model
name with public hosted models.

### Type of change

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

---------

Co-authored-by: 0000sir <0000sir@gmail.com>
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

rag/llm/sequence2txt_model.py

@@ -90,6 +90,7 @@ class XinferenceSeq2txt(Base):
     def __init__(self,key,model_name="whisper-small",**kwargs):
         self.base_url = kwargs.get('base_url', None)
         self.model_name = model_name
+        self.key = key
 
     def transcription(self, audio, language="zh", prompt=None, response_format="json", temperature=0.7):
         if isinstance(audio, str):