Update nixpkgs pins #2040

Job	Run time
check-materialization-concurrency	21s
cabal-doExactConfig	1m 32s
cabal	1m 30s
build-extra-hackages	13s
check-path-support	1m 13s
closure-size	3s
docs	28s
haskell-nix-roots-do-not-require-IFDs	5s
hix	1m 6s
hix-cabal	17s
hydra-ifdLevel-0-and-1	31s
hydra-ifdLevel-2	20s
hydra-ifdLevel-3-and-ghc-8-10	19s
hydra-ifdLevel-3-and-ghc-9-2	23s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	6s
hydra-without-remote-builders	15s
maintainer-scripts	5s
multi-target	11s
nix-build	53m 28s
nix-tools	9s
plan-extra-hackages	5s
runghc	21s
shellFor-hoogle	7s
shellFor-multiple-package	9s
shellFor-single-package	13s
tests-benchmarks	6s
shellFor-not-depends	14s
unit-tests	3s
update-docs	4s
	1h 3m 57s

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