Use unit id for package key #2470

Job	Run time
build-extra-hackages	31s
cabal	36s
cabal-doExactConfig	31s
docs	25s
hix	24s
hydra-ifdLevel-0-and-1	28s
maintainer-scripts	14s
multi-target	14s
nix-build	12s
plan-extra-hackages	12s
runghc	11s
shellFor-multiple-package	14s
shellFor-not-depends	10s
shellFor-hoogle	10s
shellFor-single-package	10s
tests-benchmarks	12s
unit-tests	9s
check-materialization-concurrency	21s
check-path-support	7s
closure-size	3s
haskell-nix-roots-do-not-require-IFDs	5s
hix-cabal	16s
hydra-ifdLevel-2	20s
hydra-ifdLevel-3-and-ghc-8-10	23s
hydra-ifdLevel-3-and-ghc-9-2	20s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	14s
hydra-without-remote-builders-ghc8107	21s
hydra-without-remote-builders-ghc9101	20s
nix-tools	9s
update-docs	4s
	8m 6s

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