Use unit id for package key #2523

Job	Run time
build-extra-hackages	24s
cabal	29s
closure-size	9s
docs	1m 10s
cabal-doExactConfig	29s
hix	1m 23s
hydra-ifdLevel-0-and-1	37s
hydra-ifdLevel-2	24s
hydra-ifdLevel-3-and-ghc-8-10	22s
hydra-ifdLevel-3-and-ghc-9-2	35s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	20s
maintainer-scripts	28s
multi-target	55s
nix-build	1m 15s
plan-extra-hackages	19s
runghc	21s
shellFor-hoogle	24s
shellFor-multiple-package	34s
shellFor-not-depends	49s
tests-benchmarks	36s
shellFor-single-package	44s
unit-tests	30s
update-docs	13s
check-materialization-concurrency	31s
check-path-support	20s
haskell-nix-roots-do-not-require-IFDs	17s
hix-cabal	16s
hydra-without-remote-builders-ghc8107	1m 5s
hydra-without-remote-builders-ghc9101	48s
nix-tools	22s
	17m 9s

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