Use unit id for package key #2507

Job	Run time
cabal	1m 35s
cabal-doExactConfig	1m 31s
build-extra-hackages	1m 32s
check-materialization-concurrency	24s
check-path-support	1m 3s
closure-size	9s
docs	2m 27s
haskell-nix-roots-do-not-require-IFDs	48s
hix	2m 38s
hix-cabal	5m 2s
hydra-ifdLevel-0-and-1	1m 58s
hydra-ifdLevel-2	44s
hydra-ifdLevel-3-and-ghc-8-10	44s
hydra-ifdLevel-3-and-ghc-9-2	30s
hydra-without-remote-builders-ghc8107	2m 17s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	24s
hydra-without-remote-builders-ghc9101	3m 28s
maintainer-scripts	18s
multi-target	21s
nix-build	40s
nix-tools	3m 44s
plan-extra-hackages	17s
runghc	18s
shellFor-hoogle	33s
shellFor-multiple-package	24s
shellFor-not-depends	21s
shellFor-single-package	24s
tests-benchmarks	28s
unit-tests	23s
update-docs	12s
	35m 37s

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