agents: fix the function call of openai llm.

[chainhelen]

According to the guides of openai function call, Once you've executed these function calls in your application, you can provide the result back to the model by adding one new message to the conversation for each function call, each containing the result of one function call, with a tool_call_id referencing the id from tool_calls. We need to provide the function call result back to the model in line with the specified structure, otherwise the openai server will verify the parameters and return a 400 status code.

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[chainhelen]

If I use agents with function call response by openai llm gpt-4o-2024-05-13, langchaingo will get 400 status code, and the TestExecutorWithOpenAIFunctionAgent also can reproduce this issue
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This commit fix this

[avi3tal]

+1 for this fix. otherwise openai agent is broken