Use unit id for package key #2521

Job	Run time
build-extra-hackages	4m 29s
cabal-doExactConfig	10m 42s
cabal	10m 37s
check-materialization-concurrency	24s
closure-size	9s
docs	2m 54s
hix	33m 27s
hydra-ifdLevel-0-and-1	25s
hydra-ifdLevel-2	22s
hydra-ifdLevel-3-and-ghc-8-10	28s
hydra-ifdLevel-3-and-ghc-9-2	28s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	20s
maintainer-scripts	1m 21s
multi-target	34m 20s
nix-build	53m 21s
plan-extra-hackages	40s
runghc	48s
shellFor-hoogle	33m 47s
shellFor-multiple-package	7m 19s
tests-benchmarks	23s
unit-tests	16s
shellFor-single-package	31s
shellFor-not-depends	29s
update-docs	8s
check-path-support	22s
haskell-nix-roots-do-not-require-IFDs	9s
hix-cabal	4m 47s
hydra-without-remote-builders-ghc8107	1m 28s
hydra-without-remote-builders-ghc9101	3m 43s
nix-tools	2m 41s
	3h 31m 18s

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