Disable aarch64-linux on hydra #2481

Job	Run time
nix-build	1m 49s
cabal	29s
unit-tests	12s
runghc	19s
plan-extra-hackages	14s
multi-target	42s
maintainer-scripts	10s
cabal-doExactConfig	18s
shellFor-hoogle	22s
shellFor-multiple-package	27s
shellFor-not-depends	19s
shellFor-single-package	27s
tests-benchmarks	20s
build-extra-hackages	26s
check-materialization-concurrency	23s
check-path-support	16s
closure-size	8s
docs	41s
haskell-nix-roots-do-not-require-IFDs	7s
hix	1m 1s
hydra-ifdLevel-0-and-1	41s
hydra-ifdLevel-2	22s
hydra-ifdLevel-3-and-ghc-8-10	16s
hydra-ifdLevel-3-and-ghc-9-2	23s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	18s
hydra-without-remote-builders-ghc8107	1m 18s
update-docs	4s
hix-cabal	2m 58s
hydra-without-remote-builders-ghc9101	1m 5s
nix-tools	17s
	16m 52s

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