[Bugfix] Fix v1/spec_decode/test_ngram.py

[zixi-qi]

Fix v1/spec_decode/test_ngram.py which is currently broken in trunk

Test Plan:
Before:

$ pytest -v tests/v1/spec_decode/test_ngram.py
===================================================================== test session starts =====================================================================
platform linux -- Python 3.12.10, pytest-8.3.5, pluggy-1.5.0 -- /home/qizixi/uv_env/vllm/bin/python
cachedir: .pytest_cache
rootdir: /data/users/qizixi/gitrepos/qizixi/vllm
configfile: pyproject.toml
plugins: anyio-4.9.0
collected 3 items                                                                                                                                             

tests/v1/spec_decode/test_ngram.py::test_kmp_lps_array PASSED                                                                                           [ 33%]
tests/v1/spec_decode/test_ngram.py::test_find_subarray_kmp PASSED                                                                                       [ 66%]
tests/v1/spec_decode/test_ngram.py::test_ngram_proposer FAILED                                                                                          [100%]

========================================================================== FAILURES ===========================================================================
_____________________________________________________________________ test_ngram_proposer _____________________________________________________________________

    def test_ngram_proposer():
>       proposer = NgramProposer()
E       TypeError: NgramProposer.__init__() missing 1 required positional argument: 'vllm_config'

tests/v1/spec_decode/test_ngram.py:42: TypeError
====================================================================== warnings summary =======================================================================
<frozen importlib._bootstrap>:488
  <frozen importlib._bootstrap>:488: DeprecationWarning: Type google._upb._message.MessageMapContainer uses PyType_Spec with a metaclass that has custom tp_new. This is deprecated and will no longer be allowed in Python 3.14.

<frozen importlib._bootstrap>:488
  <frozen importlib._bootstrap>:488: DeprecationWarning: Type google._upb._message.ScalarMapContainer uses PyType_Spec with a metaclass that has custom tp_new. This is deprecated and will no longer be allowed in Python 3.14.

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=================================================================== short test summary info ===================================================================
FAILED tests/v1/spec_decode/test_ngram.py::test_ngram_proposer - TypeError: NgramProposer.__init__() missing 1 required positional argument: 'vllm_config'
=========================================================== 1 failed, 2 passed, 2 warnings in 1.52s ===========================================================

After:

$ pytest -v tests/v1/spec_decode/test_ngram.py
===================================================================== test session starts =====================================================================
platform linux -- Python 3.12.10, pytest-8.3.5, pluggy-1.5.0 -- /home/qizixi/uv_env/vllm/bin/python
cachedir: .pytest_cache
rootdir: /data/users/qizixi/gitrepos/qizixi/vllm
configfile: pyproject.toml
plugins: anyio-4.9.0
collected 3 items                                                                                                                                             
tests/v1/spec_decode/test_ngram.py::test_kmp_lps_array PASSED                                                                                           [ 33%]
tests/v1/spec_decode/test_ngram.py::test_find_subarray_kmp PASSED                                                                                       [ 66%]
tests/v1/spec_decode/test_ngram.py::test_ngram_proposer PASSED                                                                                          [100%]
====================================================================== warnings summary =======================================================================
<frozen importlib._bootstrap>:488
  <frozen importlib._bootstrap>:488: DeprecationWarning: Type google._upb._message.MessageMapContainer uses PyType_Spec with a metaclass that has custom tp_new. This is deprecated and will no longer be allowed in Python 3.14.
<frozen importlib._bootstrap>:488
  <frozen importlib._bootstrap>:488: DeprecationWarning: Type google._upb._message.ScalarMapContainer uses PyType_Spec with a metaclass that has custom tp_new. This is deprecated and will no longer be allowed in Python 3.14.
-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
================================================================ 3 passed, 2 warnings in 1.68s ================================================================

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[WoosukKwon]

LGTM! Thanks for the fix. Just realized that v1/spec_decode was omitted from the tests.