fix: serialize boolean provider params as lowercase strings

str(True) produces "True" but Mistral API expects lowercase "true".
Use str(value).lower() for bool params in provider-specific fields.

litellm/llms/mistral/audio_transcription/transformation.py

@@ -121,7 +121,7 @@ class MistralAudioTranscriptionConfig(BaseAudioTranscriptionConfig):
             openai_params=self.get_supported_openai_params(model),
         )
         for key, value in provider_specific_params.items():
-            form_fields[key] = str(value)
+            form_fields[key] = str(value).lower() if isinstance(value, bool) else str(value)
 
         files = {
             "file": (

tests/test_litellm/llms/mistral/audio_transcription/test_mistral_audio_transcription_transformation.py

@@ -141,7 +141,7 @@ def test_mistral_audio_transcription_request_with_diarize():
     audio_file.close()
 
     assert isinstance(result.data, dict)
-    assert result.data["diarize"] == "True"
+    assert result.data["diarize"] == "true"
 
 
 def test_mistral_audio_transcription_response_transform():