Use unit id for package key #2473

Job	Run time
cabal	3m 18s
nix-build	3m 17s
runghc	15s
unit-tests	18s
cabal-doExactConfig	3m 22s
maintainer-scripts	1m 55s
multi-target	50s
plan-extra-hackages	18s
shellFor-hoogle	26s
shellFor-multiple-package	22s
shellFor-single-package	21s
shellFor-not-depends	21s
tests-benchmarks	22s
build-extra-hackages	18s
check-materialization-concurrency	25s
check-path-support	12s
closure-size	6s
docs	1m 20s
haskell-nix-roots-do-not-require-IFDs	58s
hix	1m 7s
hydra-ifdLevel-0-and-1	46s
hydra-ifdLevel-2	27s
hydra-ifdLevel-3-and-ghc-8-10	18s
hydra-ifdLevel-3-and-ghc-9-2	23s
hydra-without-remote-builders-ghc8107	15s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	25s
hydra-without-remote-builders-ghc9101	16s
update-docs	10s
hix-cabal	13s
nix-tools	15s
	23m 19s

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