Use unit id for package key #2567

Job	Run time
cabal-doExactConfig	4m 51s
build-extra-hackages	4m 37s
cabal	3m 36s
check-materialization-concurrency	22s
check-path-support	4m 1s
closure-size	3s
docs	5m 12s
haskell-nix-roots-do-not-require-IFDs	9m 30s
hix	1m 47s
hix-cabal	26s
hydra-ifdLevel-0-and-1	11m 38s
hydra-ifdLevel-2	17m 41s
hydra-ifdLevel-3	30m 10s
hydra-without-remote-builders-ghc8107	3m 41s
hydra-without-remote-builders-ghc9101	4m 14s
maintainer-scripts	19s
multi-target	1m 28s
nix-build	16m 36s
nix-tools	3m 32s
plan-extra-hackages	4m 3s
runghc	3m 34s
shellFor-hoogle	4m 44s
shellFor-not-depends	10s
shellFor-multiple-package	15s
shellFor-single-package	13s
tests-benchmarks	9s
unit-tests	5s
update-docs	7s
	2h 17m 4s

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