Use unit id for package key #2542

Job	Run time
cabal	3m 53s
build-extra-hackages	3m 45s
cabal-doExactConfig	3m 49s
check-materialization-concurrency	25s
check-path-support	2m 46s
closure-size	8s
haskell-nix-roots-do-not-require-IFDs	1m 7s
hix	4m 35s
docs	1m 15s
hix-cabal	1m 45s
hydra-ifdLevel-0-and-1	15s
hydra-ifdLevel-3-and-ghc-8-10	13s
hydra-ifdLevel-2	14s
hydra-ifdLevel-3-and-ghc-9-2	13s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	12s
hydra-without-remote-builders-ghc8107	2m 44s
hydra-without-remote-builders-ghc9101	2m 30s
maintainer-scripts	14s
multi-target	4m 20s
nix-build	2m 1s
nix-tools	14s
plan-extra-hackages	16s
runghc	19s
shellFor-hoogle	1m 28s
shellFor-multiple-package	1m 5s
shellFor-not-depends	24s
shellFor-single-package	27s
tests-benchmarks	19s
unit-tests	13s
update-docs	8s
	41m 17s

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