Use unit id for package key #2539

Job	Run time
build-extra-hackages	18s
cabal	24s
cabal-doExactConfig	25s
closure-size	8s
docs	32s
hix	31s
hydra-ifdLevel-2	12s
hydra-ifdLevel-0-and-1	12s
hydra-ifdLevel-3-and-ghc-8-10	14s
hydra-ifdLevel-3-and-ghc-9-2	15s
maintainer-scripts	21s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	19s
multi-target	51s
nix-build	1m 57s
plan-extra-hackages	19s
runghc	19s
shellFor-hoogle	18s
shellFor-multiple-package	20s
shellFor-not-depends	29s
shellFor-single-package	30s
tests-benchmarks	16s
unit-tests	12s
update-docs	7s
check-materialization-concurrency	23s
check-path-support	10s
haskell-nix-roots-do-not-require-IFDs	8s
hix-cabal	13s
hydra-without-remote-builders-ghc8107	1m 21s
hydra-without-remote-builders-ghc9101	1m 21s
nix-tools	13s
	13m 18s

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