Add GHC 9.12.1 #2836

Job	Run time
nix-build	50s
unit-tests	10s
cabal	14s
build-extra-hackages	11s
cabal-doExactConfig	13s
check-materialization-concurrency	23s
check-path-support	8s
closure-size	5s
docs	32s
haskell-nix-roots-do-not-require-IFDs	13s
hix	39s
hydra-ifdLevel-0-and-1	9m 48s
hydra-ifdLevel-2	3m 32s
hydra-ifdLevel-3	4m 20s
hydra-without-remote-builders-ghc8107	15s
maintainer-scripts	16s
multi-target	44s
plan-extra-hackages	7s
runghc	11s
shellFor-hoogle	12s
shellFor-multiple-package	14s
shellFor-not-depends	14s
shellFor-single-package	29s
tests-benchmarks	7s
update-docs	5s
hix-cabal	9s
hydra-without-remote-builders-ghc9101	17s
nix-tools	20s
	24m 58s

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