Add musl build action #29

Job	Run time
Build macOS universal binary	2m 41s
Build x86_64-unknown-linux-musl	40s
Build aarch64-unknown-linux-musl	41s
Build i686-pc-windows-msvc	3m 39s
Build i686-unknown-linux-gnu	2m 47s
Build aarch64-unknown-linux-gnu	2m 41s
Build x86_64-pc-windows-msvc	3m 0s
Build x86_64-unknown-linux-gnu	2m 29s
Build armv7-unknown-linux-gnueabihf	2m 42s
	21m 20s

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