[v0.9.1][Bugfix] Fix guided decoding invalid backend

[shen-shanshan]

What this PR does / why we need it?

Run:

pytest -sv tests/singlecard/test_guided_decoding.py

Come across an error:

FAILED tests/singlecard/test_guided_decoding.py::test_guided_json_completion[guidance:disable-any-whitespace] - NotImplementedError: VLLM_USE_V1=1 is not supported with --guided-decoding-backend=guidance:disable-any-whitespace.
FAILED tests/singlecard/test_guided_decoding.py::test_guided_regex[guidance:disable-any-whitespace] - NotImplementedError: VLLM_USE_V1=1 is not supported with --guided-decoding-backend=guidance:disable-any-whitespace.

Does this PR introduce any user-facing change?

How was this patch tested?

Run:

pytest -sv tests/singlecard/test_guided_decoding.py

Output:

=========================================================================== test session starts ===========================================================================
platform linux -- Python 3.10.18, pytest-8.4.1, pluggy-1.6.0
rootdir: /home/sss/github/vllm-v0.9.1/vllm-ascend
configfile: pytest.ini
plugins: anyio-4.10.0, mock-3.14.1
collected 8 items                                                                                                                                                         

tests/singlecard/test_guided_decoding.py ss.ss..s                                                                                                                   [100%]

============================================================================ warnings summary =============================================================================
<frozen importlib._bootstrap>:241
  <frozen importlib._bootstrap>:241: DeprecationWarning: builtin type SwigPyPacked has no __module__ attribute

<frozen importlib._bootstrap>:241
  <frozen importlib._bootstrap>:241: DeprecationWarning: builtin type SwigPyObject has no __module__ attribute

../../../miniconda3/envs/vllm-v0.9.1/lib/python3.10/site-packages/torch_npu/dynamo/torchair/__init__.py:8
  /home/sss/miniconda3/envs/vllm-v0.9.1/lib/python3.10/site-packages/torch_npu/dynamo/torchair/__init__.py:8: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
    import pkg_resources

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
========================================================== 3 passed, 5 skipped, 3 warnings in 193.21s (0:03:13) ===========================================================

[gemini-code-assist]

Code Review

This pull request addresses a bug in the guided decoding tests where an invalid backend, guidance:disable-any-whitespace, was causing failures when running with VLLM_USE_V1=1. The fix correctly replaces the invalid backend with guidance, which resolves the NotImplementedError and allows the tests to pass as expected. The change is minimal, targeted, and effectively resolves the issue.

[Yikun]

so just a test fixed? Why it was failure in history CI?

[shen-shanshan]

so just a test fixed? Why it was failure in history CI?

I am also comfused about this. 😂 How does the CI passed in history v0.9.1 PR?

[MengqingCao]

How much time does this case cost? if it is reasonable, I think we'd better keep it running, as the CI on v0.9.1-dev actually is not too much

[shen-shanshan]

maybe 10+ minutes...

[MengqingCao]

Okay, then let's keep it skipped