Use unit id for package key #2478

Job	Run time
cabal	19s
build-extra-hackages	19s
cabal-doExactConfig	19s
closure-size	4s
docs	36s
hix	51s
hydra-ifdLevel-0-and-1	41s
hydra-ifdLevel-2	18s
hydra-ifdLevel-3-and-ghc-8-10	34s
hydra-ifdLevel-3-and-ghc-9-2	41s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	36s
maintainer-scripts	24s
multi-target	27s
nix-build	30s
plan-extra-hackages	28s
runghc	31s
shellFor-hoogle	22s
shellFor-multiple-package	20s
shellFor-not-depends	19s
shellFor-single-package	18s
tests-benchmarks	14s
unit-tests	11s
check-materialization-concurrency	20s
check-path-support	9s
haskell-nix-roots-do-not-require-IFDs	4s
hix-cabal	11s
hydra-without-remote-builders-ghc8107	14s
hydra-without-remote-builders-ghc9101	15s
nix-tools	14s
update-docs	5s
	10m 54s

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