Use unit id for package key #2516

Job	Run time
cabal	14s
cabal-doExactConfig	14s
multi-target	15s
nix-build	13s
runghc	14s
tests-benchmarks	14s
unit-tests	14s
build-extra-hackages	13s
docs	31s
hix	51s
hydra-ifdLevel-0-and-1	35s
maintainer-scripts	14s
plan-extra-hackages	14s
shellFor-hoogle	13s
shellFor-multiple-package	15s
shellFor-not-depends	13s
shellFor-single-package	14s
check-materialization-concurrency	24s
check-path-support	8s
closure-size	7s
haskell-nix-roots-do-not-require-IFDs	8s
hydra-ifdLevel-2	17s
hydra-ifdLevel-3-and-ghc-8-10	18s
hydra-ifdLevel-3-and-ghc-9-2	19s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	20s
hydra-without-remote-builders-ghc8107	30s
update-docs	8s
hydra-without-remote-builders-ghc9101	24s
hix-cabal	10s
nix-tools	12s
	8m 36s

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