ci: Fix quick-jobs GHC version to 9.6 (backport #10026)

[mergify]

This should fix the CI quick jobs that have been failing recently. Could you please have a look @Mikolaj

---

This is an automatic backport of pull request #10026 done by Mergify.

[mergify]

Cherry-pick of 305033b has failed:

On branch mergify/bp/3.12/pr-10026
Your branch is up to date with 'origin/3.12'.

You are currently cherry-picking commit 305033b30.
  (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/quick-jobs.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

[Mikolaj]

Uh-oh.

[Mikolaj]

I guess we are missing some earlier CI backport that touches quick-jobs.yml.

[ulysses4ever]

I'm doing it manually in #10043