Update nixpkgs pins #2581

Job	Run time
cabal	10s
cabal-doExactConfig	9s
build-extra-hackages	6s
check-materialization-concurrency	20s
check-path-support	5s
closure-size	3s
docs	22s
hix	34s
hydra-ifdLevel-0-and-1	2m 9s
hydra-ifdLevel-2	32s
maintainer-scripts	7s
hydra-ifdLevel-3	39s
multi-target	30s
nix-build	40m 43s
plan-extra-hackages	6s
runghc	7s
shellFor-hoogle	11s
shellFor-multiple-package	10s
shellFor-not-depends	14s
shellFor-single-package	14s
tests-benchmarks	13s
unit-tests	4s
update-docs	6s
haskell-nix-roots-do-not-require-IFDs	34m 20s
hix-cabal	7s
hydra-without-remote-builders-ghc8107	11s
hydra-without-remote-builders-ghc9101	11s
nix-tools	10s
	1h 22m 53s

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