Update musl.nix (enableSystemd -> systemdSupport) #2930

Job	Run time
nix-build	7m 37s
runghc	59s
unit-tests	5s
cabal	56s
cabal-doExactConfig	53s
multi-target	1m 34s
shellFor-hoogle	1m 4s
shellFor-multiple-package	53s
shellFor-not-depends	55s
shellFor-single-package	26s
tests-benchmarks	9s
build-extra-hackages	9s
docs	2m 10s
hix	7m 46s
hydra-ifdLevel-0-and-1	6m 2s
maintainer-scripts	7s
plan-extra-hackages	6s
check-path-support	11s
check-materialization-concurrency	19s
closure-size	7s
haskell-nix-roots-do-not-require-IFDs	1m 26s
hydra-ifdLevel-2	5m 26s
hydra-ifdLevel-3	30m 11s
update-docs	4s
hix-cabal	6m 0s
hydra-without-remote-builders-ghc9101	4m 23s
hydra-without-remote-builders-ghc966	2m 27s
nix-tools	12s
	1h 22m 37s

Provide feedback