fix tts add bug (#2224)

### What problem does this PR solve?

fix tts add bug

### Type of change

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

---------

Co-authored-by: Zhedong Cen <cenzhedong2@126.com>

api/apps/llm_app.py

             key=llm["api_key"], model_name=llm["llm_name"], base_url=llm["api_base"]
         )
         try:
-            for resp in mdl.transcription("Hello~ Ragflower!"):
+            for resp in mdl.tts("Hello~ Ragflower!"):
                 pass
         except RuntimeError as e:
             msg += f"\nFail to access model({llm['llm_name']})." + str(e)