Issue: fix the issue #11648 init minimax llm (#12554)

e https://github.com/langchain-ai/langchain/issues/11648 Minimax
llm failed to initialize

The idea of this fix is
https://github.com/langchain-ai/langchain/issues/10917#issuecomment-1765606725

do not use  underscore in python model class

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Co-authored-by: zhuojianming@cmcm.com <zhuojianming@cmcm.com>
Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/langchain/langchain/llms/minimax.py

@@ -56,7 +56,7 @@ class _MinimaxEndpointClient(BaseModel):
 class MinimaxCommon(BaseModel):
     """Common parameters for Minimax large language models."""
 
-    _client: _MinimaxEndpointClient
+    _client: Any = None
     model: str = "abab5.5-chat"
     """Model name to use."""
     max_tokens: int = 256