Use unit id for package key #2526

Job	Run time
unit-tests	23s
nix-build	1m 18s
runghc	30s
cabal	29s
cabal-doExactConfig	28s
check-path-support	14s
build-extra-hackages	26s
docs	1m 9s
hydra-ifdLevel-0-and-1	25s
closure-size	10s
hix	56s
hydra-ifdLevel-2	25s
hydra-ifdLevel-3-and-ghc-8-10	20s
hydra-ifdLevel-3-and-ghc-9-2	18s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	18s
maintainer-scripts	22s
multi-target	52s
plan-extra-hackages	20s
shellFor-hoogle	36s
shellFor-multiple-package	38s
shellFor-not-depends	36s
shellFor-single-package	28s
tests-benchmarks	18s
update-docs	8s
check-materialization-concurrency	26s
haskell-nix-roots-do-not-require-IFDs	8s
hix-cabal	10s
hydra-without-remote-builders-ghc9101	29s
hydra-without-remote-builders-ghc8107	37s
nix-tools	14s
	14m 11s

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