Fix workflows for PRs (backport #135)

[mergify]

This is an automatic backport of pull request #135 done by Mergify.
Cherry-pick of 5dfd401 has failed:

On branch mergify/bp/humble/pr-135
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit 5dfd401.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   .github/workflows/sphinx-check-warnings-pr.yml

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   .github/workflows/reusable-sphinx-check-single-version.yml
	deleted by us:   .github/workflows/sphinx-check-links.yml
	deleted by us:   .github/workflows/sphinx-check-warnings.yml
	both modified:   .github/workflows/sphinx-make-page.yml
	both modified:   make_help_scripts/add_tmp_commits

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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