openai, azure: update model_name in ChatResult to use name from API response (#22569)

The response.get("model", self.model_name) checks if the model key
exists in the response dictionary. If it does, it uses that value;
otherwise, it uses self.model_name.

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---------

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

libs/partners/openai/langchain_openai/chat_models/base.py

@@ -581,7 +581,7 @@ class BaseChatOpenAI(BaseChatModel):
             generations.append(gen)
         llm_output = {
             "token_usage": token_usage,
-            "model_name": self.model_name,
+            "model_name": response.get("model", self.model_name),
             "system_fingerprint": response.get("system_fingerprint", ""),
         }
         return ChatResult(generations=generations, llm_output=llm_output)