Update nixpkgs pins #3425

Job	Run time
nix-build	3m 4s
unit-tests	12s
maintainer-scripts	12s
runghc	1m 27s
plan-extra-hackages	13s
shellFor-hoogle	1m 46s
cabal-doExactConfig	14s
shellFor-multiple-package	19s
shellFor-not-depends	23s
tests-benchmarks	13s
cabal	14s
multi-target	59s
shellFor-single-package	24s
check-path-support	20s
haskell-nix-roots-do-not-require-IFDs	31s
build-extra-hackages	12s
hydra-ifdLevel-2	6m 35s
hix	1m 15s
hydra-without-remote-builders-ghc967	9s
hydra-without-remote-builders-ghc9102	8s
docs	1m 21s
check-nix-tools	17s
hydra-ifdLevel-0-and-1	2m 56s
closure-size	7s
hydra-ifdLevel-3	8m 32s
hix-cabal	16s
check-materialization-concurrency	23s
update-docs	9s
	32m 51s

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