This allows all of the tests in `test_proxy_server.py` to pass, with the
exception of `test_load_router_config`, without needing to set up real
environment variables.
Before:
```shell
$ env -i PATH=$PATH poetry run pytest litellm/tests/test_proxy_server.py -k 'not test_load_router_config' --disable-warnings
...
========================================================== short test summary info ===========================================================
ERROR litellm/tests/test_proxy_server.py::test_bedrock_embedding - openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY enviro...
ERROR litellm/tests/test_proxy_server.py::test_chat_completion - openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY enviro...
ERROR litellm/tests/test_proxy_server.py::test_chat_completion_azure - openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY enviro...
ERROR litellm/tests/test_proxy_server.py::test_chat_completion_optional_params - openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY enviro...
ERROR litellm/tests/test_proxy_server.py::test_embedding - openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY enviro...
ERROR litellm/tests/test_proxy_server.py::test_engines_model_chat_completions - openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY enviro...
ERROR litellm/tests/test_proxy_server.py::test_health - openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY enviro...
ERROR litellm/tests/test_proxy_server.py::test_img_gen - openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY enviro...
ERROR litellm/tests/test_proxy_server.py::test_openai_deployments_model_chat_completions_azure - openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY enviro...
========================================== 2 skipped, 1 deselected, 39 warnings, 9 errors in 3.24s ===========================================
```
After:
```shell
$ env -i PATH=$PATH poetry run pytest litellm/tests/test_proxy_server.py -k 'not test_load_router_config' --disable-warnings
============================================================ test session starts =============================================================
platform darwin -- Python 3.12.3, pytest-7.4.4, pluggy-1.5.0
rootdir: /Users/abramowi/Code/OpenSource/litellm
plugins: anyio-4.3.0, asyncio-0.23.6, mock-3.14.0
asyncio: mode=Mode.STRICT
collected 12 items / 1 deselected / 11 selected
litellm/tests/test_proxy_server.py s.........s [100%]
========================================== 9 passed, 2 skipped, 1 deselected, 48 warnings in 8.42s ===========================================
```
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