Support GHC 9.10.1

[tchoutri]

cc @treeowl

[Bodigrim]

Given that there were no developments in master since the release of unordered-containers-0.2.20, let me use my Hackage Trustee powers and make a revision, because otherwise it blocks lots of work:

https://hackage.haskell.org/package/unordered-containers-0.2.20/revisions/

@treeowl hopefully it's alright with you. I checked that the test suite compiles and passes.

[treeowl]

Sorry, I've been underwater with family stuff. Dunno about @sjakobi .

[tchoutri]

@sjakobi I'd really appreciate if you or another maintainer could pull the lever on this one. :)

[andreasabel]

@sjakobi seems to have submerged, so maybe this package should get another co-maintainer.

Anyway, this PR is outdated and should be closed.

• Make CI work again and bump to 9.12.2 #499

[sjakobi]

Sorry for the long absence, everyone. I'm back for now, but I agree that having another co-maintainer for this package would be a good idea.

[tchoutri]

@sjakobi Thanks! You should definitely advertise this on Discourse. :)