Change wrong kwargs name (#1435)

Fix #1434 by changing the argument name to
`LangChainChatModelCompletionFn` in the registry.

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evals/registry/completion_fns/langchain_llms.yaml

@@ -23,5 +23,5 @@ langchain/chat_model/gpt-3.5-turbo:
  class: evals.completion_fns.langchain_llm:LangChainChatModelCompletionFn
  args:
  llm: ChatOpenAI
- chat_model_kwargs:
+ llm_kwargs:
  model_name: gpt-3.5-turbo