[CI] Use correct ref for scheduled workflows (backport #1013)

[mergify]

This is an automatic backport of pull request #1013 done by Mergify.
Cherry-pick of 737a45b has failed:

On branch mergify/bp/humble/pr-1013
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit 737a45b.
  (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)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   .github/workflows/humble-debian-build.yml
	both modified:   .github/workflows/humble-rhel-binary-build.yml
	deleted by us:   .github/workflows/iron-debian-build.yml
	deleted by us:   .github/workflows/iron-rhel-binary-build.yml
	deleted by us:   .github/workflows/rolling-debian-build.yml
	both modified:   .github/workflows/rolling-rhel-binary-build.yml

no changes added to commit (use "git add" and/or "git commit -a")

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

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[christophfroehlich]

needs #1016 first

[mergify]

This pull request is in conflict. Could you fix it @bmagyar @destogl @christophfroehlich?