ci: build also on macOS #202

Job	Run time
cross +1.85 build riscv64gc-unknown-linux-gnu	1m 26s
cross +1.85 build aarch64-unknown-linux-gnu	2m 4s
cross +stable build armv7-unknown-linux-gnueabihf	1m 57s
cross +1.85 build armv7-unknown-linux-gnueabihf	2m 10s
cross +stable build riscv64gc-unknown-linux-gnu	1m 6s
cross +stable build aarch64-unknown-linux-gnu	1m 54s
	10m 37s

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