Use unit id for package key #2532

Job	Run time
cabal	20s
closure-size	7s
cabal-doExactConfig	20s
build-extra-hackages	18s
docs	30s
hix	34s
hydra-ifdLevel-0-and-1	13s
hydra-ifdLevel-2	14s
hydra-ifdLevel-3-and-ghc-8-10	13s
hydra-ifdLevel-3-and-ghc-9-2	13s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	12s
maintainer-scripts	15s
multi-target	44s
nix-build	16s
plan-extra-hackages	16s
runghc	19s
shellFor-multiple-package	18s
shellFor-hoogle	10s
shellFor-not-depends	11s
shellFor-single-package	11s
tests-benchmarks	20s
unit-tests	13s
check-materialization-concurrency	26s
check-path-support	8s
haskell-nix-roots-do-not-require-IFDs	7s
hix-cabal	9s
hydra-without-remote-builders-ghc8107	12s
hydra-without-remote-builders-ghc9101	12s
nix-tools	11s
update-docs	8s
	8m 0s

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