Add Linux ARM64 musl release assets

Delta currently releases an x86_64 musl asset, but not an aarch64-unknown-linux-musl asset.

I validated a proposed native ARM64 release path on a fork. It builds and packages the target on GitHub's ubuntu-24.04-arm runner using musl-tools, and the complete package job passed:

https://github.com/meop/delta/actions/runs/33445796393/job/99664497180

The change would add the ARM64 musl target alongside the existing x86_64 musl release, while retaining the existing archive and Debian-package conventions.

Would a focused PR for this additional Linux ARM64 musl release asset be welcome?