Add GHC 9.12.1 #2838

Job	Run time
nix-build	4m 23s
unit-tests	6s
cabal	2m 14s
cabal-doExactConfig	1m 37s
multi-target	2m 43s
shellFor-single-package	1m 43s
tests-benchmarks	1m 55s
build-extra-hackages	1m 37s
maintainer-scripts	38s
plan-extra-hackages	5s
runghc	7s
shellFor-hoogle	8s
shellFor-multiple-package	12s
shellFor-not-depends	10s
check-materialization-concurrency	19s
check-path-support	9s
closure-size	2s
haskell-nix-roots-do-not-require-IFDs	1m 33s
docs	1m 35s
hix	3m 50s
hydra-ifdLevel-0-and-1	13m 26s
hydra-ifdLevel-2	10m 7s
hydra-ifdLevel-3	12m 58s
update-docs	3s
hix-cabal	1m 29s
hydra-without-remote-builders-ghc8107	12s
hydra-without-remote-builders-ghc9101	16s
nix-tools	15s
	1h 3m 52s

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