Use unit id for package key #2547

Job	Run time
cabal	1m 34s
build-extra-hackages	1m 16s
cabal-doExactConfig	1m 33s
check-materialization-concurrency	23s
closure-size	7s
check-path-support	13s
docs	48s
haskell-nix-roots-do-not-require-IFDs	11s
hix	3m 23s
hix-cabal	16s
hydra-ifdLevel-0-and-1	46s
hydra-ifdLevel-2	37s
hydra-ifdLevel-3-and-ghc-8-10	25s
hydra-ifdLevel-3-and-ghc-9-2	20s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	21s
hydra-without-remote-builders-ghc8107	2m 12s
hydra-without-remote-builders-ghc9101	2m 0s
maintainer-scripts	15s
multi-target	4m 0s
nix-build	2m 0s
nix-tools	14s
plan-extra-hackages	13s
runghc	16s
shellFor-hoogle	1m 17s
shellFor-multiple-package	19s
shellFor-not-depends	20s
shellFor-single-package	1m 46s
tests-benchmarks	15s
unit-tests	11s
update-docs	8s
	27m 39s

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