Add GHC 9.12.1 #2851

Job	Run time
build-extra-hackages	12s
cabal	11s
cabal-doExactConfig	10s
check-materialization-concurrency	22s
check-path-support	9s
closure-size	3s
docs	21s
haskell-nix-roots-do-not-require-IFDs	9s
hix	48s
hix-cabal	10s
hydra-ifdLevel-0-and-1	3m 15s
hydra-ifdLevel-2	3m 18s
hydra-ifdLevel-3	9m 25s
hydra-without-remote-builders-ghc8107	34s
hydra-without-remote-builders-ghc9101	32s
maintainer-scripts	8s
multi-target	35s
nix-build	35s
nix-tools	12s
plan-extra-hackages	10s
runghc	11s
shellFor-hoogle	9s
shellFor-multiple-package	11s
shellFor-not-depends	13s
shellFor-single-package	15s
tests-benchmarks	10s
unit-tests	5s
update-docs	5s
	22m 38s

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