Fix for older versions of nixpkgs #2962

Job	Run time
cabal	2m 21s
nix-build	19m 8s
cabal-doExactConfig	2m 23s
runghc	2m 4s
unit-tests	6s
docs	14m 52s
build-extra-hackages	47s
hix	1m 57s
hydra-ifdLevel-2	6m 56s
hydra-ifdLevel-0-and-1	3m 5s
maintainer-scripts	8s
multi-target	2m 33s
plan-extra-hackages	6s
shellFor-multiple-package	4m 49s
shellFor-not-depends	26s
shellFor-hoogle	4m 45s
shellFor-single-package	1m 37s
tests-benchmarks	14s
check-materialization-concurrency	23s
check-path-support	11s
closure-size	7s
haskell-nix-roots-do-not-require-IFDs	14s
hix-cabal	3m 0s
hydra-ifdLevel-3	30m 11s
hydra-without-remote-builders-ghc9101	3m 17s
hydra-without-remote-builders-ghc966	3m 37s
nix-tools	12s
update-docs	4s
	1h 49m 33s

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