How to add a CI badge for macos aarch64 builds?

[Max_Desiatov]

@jamieQ

i suppose it's a separate question why the most recent main branch toolchain on the download page is from a build nearly 3 weeks old.

This has been answered before: packages are usually published for all platforms at once, so builds have to be green on all platforms at once and that wasn't the case for the main branch in the last few weeks.