Add aarch64 to releases

[bigfootjon]

I want to download and use rustfmt without the rest of a rust toolchain in cases where it isn't worth setting up a whole rust toolchain (i.e. CI job to format all code, not necessarily to build everything). Adding an aarch64 release would then allow me to use the same version on my laptop for debugging with dotslash

Also, x86 support on macs is generally not the long term future for macs and aarch64 is. Let's get ahead of the deprecation of x86 by adding the new release target!

I tested this by creating a fake release in my fork, which worked correctly: https://github.com/bigfootjon/rustfmt/releases/tag/test

[ytmimi]

@bigfootjon Sorry, but we don't release rustfmt via GitHub releases anymore. The only supported release channel is via rustup since rustfmt has runtime dependencies on the installed rust toolchain.

You can get some additional context by reading the discussion on #5761