Disable ghc docs by default #2926

Job	Run time
build-extra-hackages	25m 31s
cabal	29m 44s
cabal-doExactConfig	37m 22s
check-materialization-concurrency	19s
check-path-support	38m 18s
closure-size	7s
docs	5m 45s
haskell-nix-roots-do-not-require-IFDs	1m 9s
hix	1m 39s
hix-cabal	30m 21s
hydra-ifdLevel-0-and-1	4m 13s
hydra-ifdLevel-2	2m 17s
hydra-ifdLevel-3	13m 43s
hydra-without-remote-builders-ghc9101	3m 41s
hydra-without-remote-builders-ghc966	2m 42s
maintainer-scripts	11s
multi-target	35m 37s
nix-build	1h 16m 34s
nix-tools	11s
plan-extra-hackages	26s
runghc	11m 15s
shellFor-hoogle	6m 24s
shellFor-multiple-package	2m 12s
shellFor-not-depends	32s
shellFor-single-package	1m 37s
tests-benchmarks	22s
unit-tests	8s
update-docs	4s
	5h 32m 24s

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