Add GHC 9.12.1 #2849

Job	Run time
cabal	10s
cabal-doExactConfig	13s
runghc	8s
nix-build	12m 37s
multi-target	39s
unit-tests	5s
shellFor-hoogle	8s
shellFor-not-depends	13s
shellFor-multiple-package	12s
shellFor-single-package	18s
tests-benchmarks	7s
build-extra-hackages	6s
check-materialization-concurrency	23s
closure-size	7s
docs	28s
hix	42s
hydra-ifdLevel-0-and-1	14m 14s
hydra-ifdLevel-2	3m 41s
hydra-ifdLevel-3	3m 30s
maintainer-scripts	12s
plan-extra-hackages	5s
update-docs	4s
check-path-support	6s
haskell-nix-roots-do-not-require-IFDs	18s
hix-cabal	7s
hydra-without-remote-builders-ghc8107	8s
hydra-without-remote-builders-ghc9101	8s
nix-tools	15s
	39m 24s

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