Build hadrian with ghc 9.6.6 if available. #3030

Job	Run time
build-extra-hackages	34m 9s
cabal	45m 20s
cabal-doExactConfig	38m 17s
closure-size	7s
docs	57s
hix	51m 51s
hydra-ifdLevel-0-and-1	5m 4s
hydra-ifdLevel-3	30m 15s
maintainer-scripts	10s
hydra-ifdLevel-2	5m 33s
multi-target	31m 26s
nix-build	59m 18s
plan-extra-hackages	10s
runghc	11m 15s
shellFor-hoogle	7m 16s
shellFor-not-depends	22s
shellFor-single-package	2m 31s
shellFor-multiple-package	16m 16s
tests-benchmarks	12s
unit-tests	5s
check-materialization-concurrency	19s
check-path-support	15s
haskell-nix-roots-do-not-require-IFDs	10s
hix-cabal	3m 0s
hydra-without-remote-builders-ghc9101	1m 11s
hydra-without-remote-builders-ghc966	2m 38s
nix-tools	12s
update-docs	3s
	5h 48m 22s

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