Add GHC 9.12.1 #2827

Job	Run time
nix-build	34s
runghc	13s
build-extra-hackages	8s
cabal	9s
unit-tests	5s
cabal-doExactConfig	9s
maintainer-scripts	9s
multi-target	35s
plan-extra-hackages	6s
shellFor-hoogle	9s
shellFor-multiple-package	11s
shellFor-not-depends	12s
shellFor-single-package	15s
tests-benchmarks	7s
check-materialization-concurrency	19s
check-path-support	5s
closure-size	9s
docs	22s
haskell-nix-roots-do-not-require-IFDs	13s
hix	5m 25s
hydra-ifdLevel-0-and-1	3m 3s
hydra-ifdLevel-2	8m 32s
hydra-ifdLevel-3	30m 16s
hydra-without-remote-builders-ghc8107	2m 22s
update-docs	4s
hix-cabal	12s
hydra-without-remote-builders-ghc9101	25s
nix-tools	42s
	55m 11s

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