Update nixpkgs pins #2637

Job	Run time
cabal	10s
runghc	9s
unit-tests	5s
cabal-doExactConfig	15s
multi-target	32s
nix-build	29s
shellFor-hoogle	9s
shellFor-multiple-package	15s
shellFor-not-depends	12s
shellFor-single-package	15s
tests-benchmarks	7s
check-materialization-concurrency	20s
build-extra-hackages	6s
closure-size	7s
check-path-support	5s
docs	20s
haskell-nix-roots-do-not-require-IFDs	16s
hix	27s
hydra-ifdLevel-0-and-1	2m 31s
hydra-ifdLevel-2	2m 40s
hydra-ifdLevel-3	23m 51s
maintainer-scripts	8s
plan-extra-hackages	11s
update-docs	4s
hix-cabal	8s
hydra-without-remote-builders-ghc8107	1m 18s
hydra-without-remote-builders-ghc9101	1m 2s
nix-tools	10s
	36m 22s

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