v5

add linux/arm64 to the emulated action (#6)

The emulated companion action covers every foreign arch except aarch64, so
anyone without arm runners (self hosted x86_64 runners, plans without
ubuntu-24.04-arm) has no way to build the aarch64 AppImage.

Register the aarch64 binfmt handler the same way as the other four arches,
with a mask that ignores e_type, osabi and the ELF pad bytes uruntime
stamps AI into, so the resulting AppImage still execs. /usr/libexec/
qemu-binfmt/aarch64-binfmt-P ships in qemu-user-static, and
ghcr.io/pkgforge-dev/archlinux resolves linux/arm64 to the Arch Linux ARM
rootfs, which carries archlinux-keyring, so setup.sh needs no change.

Closes #5

Co-authored-by: Nemo <328747105+Nemo-010@users.noreply.github.com>