Mergify and actions upgrades (backport #10260)

[mergify]

Mergify is requiring different queues for different merge strategies as of mid-September.
actions/upload-artifact@v3 and actions/download-artifact@v3 are being removed in November.

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 #10260 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 75711fc has failed:

On branch mergify/bp/3.12/pr-10260
Your branch is up to date with 'origin/3.12'.

You are currently cherry-picking commit 75711fca5.
  (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:
	modified:   .github/workflows/bootstrap.yml
	modified:   .github/workflows/users-guide.yml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .github/mergify.yml
	both modified:   .github/workflows/validate.yml

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]

Note that the Mergify part does nothing, since Mergify only looks at master. But the actions are needed.