Backport #10656: Support ghc-9.12.*

[mergify]

I'm trying out -XMultilineStrings in cabal-testsuite and struck this warning, having installed ghc-9.12.1 with ghcup:

+Warning: Unknown/unsupported 'ghc' version detected (Cabal 3.15.0.0 supports 'ghc' version < 9.12):
/.../.ghcup/bin/ghc is version <GHCVER>

This pull request is the same as #9928 (that adds support for ghc-9.10.*) but bumps the GHC version once more.

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This is an automatic backport of pull request #10656 done by [Mergify](https://mergify.com).