CI: cabal-head prerelease: move to a current GitHub Action (backport #10331)

[mergify]

I don't believe we need to backport it since cabal-head only concerns master.

Explanation of the changes (based on the docs for the new action):

• title will be the same as tag (cabal-head)
• auth token has a default value that should work, I hope.

Template B: This PR does not modify behaviour or interface

E.g. the PR only touches documentation or tests, does refactorings, etc.

Include the following checklist in your PR:

• Patches conform to the coding conventions.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

---

This is an automatic backport of pull request #10331 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of db234dd has failed:

On branch mergify/bp/3.12/pr-10331
Your branch is up to date with 'origin/3.12'.

You are currently cherry-picking commit db234dde9.
  (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 <file>..." to mark resolution)
	both modified:   .github/workflows/validate.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

[geekosaur]

Backport to 3.12 needed for the LTS job.

[geekosaur]

Never mind, too many changes and this wants to be close to master for maintainability.