Build mips-unknown-linux-musl from Debian instead of Ubuntu to have access to their packages #3845

Job	Run time
cargo-deny	29s
shellcheck	9s
fmt	6s
check	18s
clippy (macos-latest)	1m 7s
generate-matrix	25s
clippy (ubuntu-latest)	32s
clippy (windows-latest)	1m 25s
test (macos-latest)	2m 1s
test (ubuntu-latest)	1m 52s
test (windows-latest)	4m 35s
bisect	0s
foreign	0s
target (${{ matrix.pretty }},${{ matrix.os }})	0s
remote	0s
podman	0s
docker-in-docker	0s
publish	0s
conclusion	2s
Coverage	8s
	13m 9s

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