Use unit id for package key #2491

Job	Run time
build-extra-hackages	36s
cabal	36s
cabal-doExactConfig	35s
check-materialization-concurrency	31s
check-path-support	24s
closure-size	17s
docs	1m 13s
haskell-nix-roots-do-not-require-IFDs	19s
hix	1m 28s
hix-cabal	25s
hydra-ifdLevel-0-and-1	1m 6s
hydra-ifdLevel-2	35s
hydra-ifdLevel-3-and-ghc-8-10	21s
hydra-ifdLevel-3-and-ghc-9-2	31s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	22s
hydra-without-remote-builders-ghc8107	15s
hydra-without-remote-builders-ghc9101	14s
maintainer-scripts	15s
multi-target	16s
nix-build	16s
nix-tools	16s
plan-extra-hackages	17s
runghc	17s
shellFor-hoogle	17s
shellFor-multiple-package	16s
shellFor-not-depends	18s
shellFor-single-package	17s
tests-benchmarks	17s
unit-tests	13s
update-docs	8s
	13m 11s

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