[generative_ai]: Function calling with OpenAI samples are not working anymore.

## In which file did you encounter the issue?
[generative_ai/function_calling/test_function_calling.py](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/main/generative_ai/function_calling/test_function_calling.py)

## Did you change the file? If so, how?

No.

## Describe the issue

Both function calling with Open AI samples ([1](https://cloud.google.com/vertex-ai/generative-ai/docs/model-reference/function-calling#python-openai), [2](https://cloud.google.com/vertex-ai/generative-ai/docs/model-reference/function-calling#python-openai_1)) are no longer working ([CI build log](https://btx.cloud.google.com/invocations/d7d20dd6-a816-43dc-8513-51f897b73d7c/log)):

```
File "/workspace/generative_ai/function_calling/test_function_calling.py", line 59, in test_function_calling_basic
response = chat_function_calling_basic.generate_text()
File "/workspace/generative_ai/function_calling/chat_function_calling_basic.py", line 39, in generate_text
client = openai.OpenAI(
File "/workspace/generative_ai/function_calling/.nox/py-3-9/lib/python3.9/site-packages/openai/_client.py", line 122, in __init__
super().__init__(
File "/workspace/generative_ai/function_calling/.nox/py-3-9/lib/python3.9/site-packages/openai/_base_client.py", line 825, in __init__
self._client = http_client or SyncHttpxClientWrapper(
File "/workspace/generative_ai/function_calling/.nox/py-3-9/lib/python3.9/site-packages/openai/_base_client.py", line 723, in __init__
super().__init__(**kwargs)
TypeError: __init__() got an unexpected keyword argument 'proxies'

- generated xml file: /workspace/generative_ai/function_calling/sponge_log.xml -
=========================== short test summary info ============================
FAILED test_function_calling.py::test_function_calling_basic - TypeError: __i...
FAILED test_function_calling.py::test_function_calling_config - TypeError: __...
========================= 2 failed, 5 passed in 14.85s =========================
```

I noticed this issue when worked on https://github.com/GoogleCloudPlatform/python-docs-samples/pull/12811
There is a related discussion https://github.com/GoogleCloudPlatform/python-docs-samples/issues/12990 about missing regressions after the recent CI migration.