move spec decode slow test to test_areas.yaml

[shanjiaz]

Purpose

Moved spec decode sloe test to test_areas.yaml. Added test was previously approved in a former PR.

Test Plan

Tested the command locally.
pytest tests/v1/spec_decode/test_acceptance_length.py -m 'slow_test'

Test Result

============================================================ test session starts =============================================================
platform linux -- Python 3.12.11, pytest-9.0.2, pluggy-1.6.0
rootdir: /home/shanjiaz/nm-vllm/vllm
configfile: pyproject.toml
plugins: anyio-4.12.1
collected 12 items / 9 deselected / 3 selected                                                                                                                                                

tests/v1/spec_decode/test_acceptance_length.py ...                                                                                                                                      [100%]

====================================================================================== warnings summary =======================================================================================
<frozen importlib._bootstrap>:488
  <frozen importlib._bootstrap>:488: DeprecationWarning: builtin type SwigPyPacked has no __module__ attribute

<frozen importlib._bootstrap>:488
  <frozen importlib._bootstrap>:488: DeprecationWarning: builtin type SwigPyObject has no __module__ attribute

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=================================================================== 3 passed, 9 deselected, 2 warnings in 448.49s (0:07:28) ==================

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request successfully moves a slow speculative decoding test to a separate Buildkite step, which will improve CI performance for the main test suite. The changes in .buildkite/test_areas/misc.yaml correctly exclude the slow test from the general test run and add a new, dedicated step to execute it. The test itself is appropriately marked. The changes are clean and achieve the intended purpose. I have no major concerns.

[mgoin]

LGTM let's see if I can trigger in CI