CI: Downgrade Cabal for GHC 8.10.7 (copy #2899)

[mergify]

Cabal 3.14 silently ignores haddock-options in cabal.project. The change is deliberate (though not warning about it probably is not). The change is documented in some places:

https://github.com/haskell/cabal/blob/master/release-notes/cabal-install-3.14.0.0.md

https://github.com/haskell/cabal/blob/master/release-notes/WIP-Cabal-3.12.x.0.md

haskell/cabal#9177

(Note that the deprecation message apparently never made it to the release notes)

We should probably think about how to fix this in the future, but for now rolling back to Cabal 3.12 will allow us to build the documentation as we want to again. The mentioned haddock-version-cpp flag in the linked cabal PR 9177 above to get a CPP define for __HADDOCK_VERSION__ did not work at all for me.

PR #2201 was supposed to update our Haddock generation to 9.0.2 but accidentally picked 8.10.7 for the uploads to Hackage, which also fixed issue #2200. I'm careful about upgrading Haddock now as I've experienced several times now that there were undocumented changes going from one version to the next that broke some rendering, and carefully rereading our complete Haddock to scan for such breakage is an impossible task. One day we'll have to upgrade, when we drop GHC 8.10 from Clash.

Still TODO:

• Write a changelog entry (see changelog/README.md)
• Check copyright notices are up to date in edited files

---

This is an automatic copy of pull request #2899 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 9d94353 has failed:

On branch mergify/copy/1.8/pr-2899
Your branch is up to date with 'origin/1.8'.

You are currently cherry-picking commit 9d94353c.
  (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:   .ci/docker/Dockerfile
	modified:   .gitlab-ci.yml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .ci/docker/build-and-publish-docker-image.sh
	both modified:   .ci/gitlab/benchmark.yml
	both modified:   .ci/gitlab/common.yml
	both modified:   .github/workflows/ci.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