Touch up release notes for cabal-install 3.12.0.0 pre-release (backport #9963)

[mergify]

Template B: This PR does not modify behaviour or interface

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

I'm touching up the release notes generated by @ffaf1 to serve as the changelog for the cabal-install 3.12.0.0 prerelease. I've mostly copied a lot of entries from the Cabal 3.12.0.0 release notes, because they significantly affect the behaviour of cabal-install as opposed to being implementation details of Cabal or changing the portions of Cabal API that are not reflected in the API and/or behaviour of cabal-install. This will require further editing effort for the official 3.12.1.0 release of cabal-install.

I checked with sort | uniq that no entries repeat and I had a quick look and couldn't find any text duplicated in the Cabal changelog that has been edited and improved and so would need to be pasted over. I also rather arbitrarily separated the changes into more and less significant, because in the original document there was no distinction (all were significant?).

• 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).

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This is an automatic backport of pull request #9963 done by [Mergify](https://mergify.com).

[Mikolaj]

A documentation-only backport. Let's see if mergify works here.

[Mikolaj]

It does, so maybe the problems with Settings branch protection got solved by making an exception for Mergify.