google-cloud-java: ci check fails at clean up step: librarian_generation_check.yaml

[zhumin8]

https://github.com/googleapis/google-cloud-java/blob/main/.github/workflows/librarian_generation_check.yaml

See log: https://github.com/googleapis/google-cloud-java/actions/runs/30375071411/job/90328519946

Node 20 is being deprecated. This workflow is running with Node 24 by default. If you need to temporarily use Node 20, you can set the ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true environment variable. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/
Post job cleanup.
(node:30815) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.
(Use `node --trace-deprecation ...` to show where the warning was created)
Error: Cache folder path is retrieved for pip but doesn't exist on disk: /home/runner/.cache/pip. This likely indicates that there are no dependencies to cache. Consider removing the cache step if it is not needed.

[JoeWang1127]

Error: Cache folder path is retrieved for pip but doesn't exist on disk: /home/runner/.cache/pip. This likely indicates that there are no dependencies to cache. Consider removing the cache step if it is not needed.

Pip is no longer a dependency anymore, see #7065

[zhumin8]

You are right, so googleapis/google-cloud-java#13912 removed the pip section from librarian.yaml,
but the actions/setup-python step from librarian_generation_check.yaml step is left-over.

2. Dangling Setup Python Action with Caching: The workflow file librarian_generation_check.yaml was updated to remove PYTHONPATH but it retained the actions/setup-python step with caching
   enabled:

   • uses: actions/setup-python@a26af69 # v5
     with:
     python-version: "3.12"
     cache: 'pip'

3. Cache Key Failure: When cache: 'pip' is specified, the actions/setup-python action automatically searches for a standard dependency file (like requirements.txt or pyproject.toml) to
   calculate a hash for the cache key. Since commit 6bdd2223211 removed all such files from the repository, the action cannot find a file to hash.

4. Post-Run Failure: While the setup phase might succeed or only log a warning, the Post Job Cleanup (where the action attempts to save the cache) fails because it lacks a valid cache key.

[zhumin8]

This is failing on each run starting today. Since it failed at post-clean up step, it did not affect test result/issue creation if any.

[JoeWang1127]

@yangyzs could you take a look at this issue?

[zhumin8]

@yangyzs & @JoeWang1127
I raised googleapis/google-cloud-java#13931 for review