Add backpack test #3062

Job	Run time
cabal	47s
build-extra-hackages	12s
cabal-doExactConfig	1m 2s
check-materialization-concurrency	20s
check-path-support	15s
closure-size	3s
docs	11m 4s
haskell-nix-roots-do-not-require-IFDs	1m 23s
hix	1m 17s
hix-cabal	3m 14s
hydra-ifdLevel-0-and-1	6m 32s
hydra-ifdLevel-2	17m 33s
hydra-ifdLevel-3	30m 17s
hydra-without-remote-builders-ghc9101	5m 36s
hydra-without-remote-builders-ghc967	20s
maintainer-scripts	6s
multi-target	37s
nix-build	6m 10s
nix-tools	12s
plan-extra-hackages	4s
runghc	17s
shellFor-hoogle	16s
shellFor-not-depends	34s
shellFor-multiple-package	46s
shellFor-single-package	39s
tests-benchmarks	12s
unit-tests	9s
update-docs	6s
	1h 30m 3s

Provide feedback