Dependencies (git, curl, builder user) are now provided by the custom act_runner image. Only su builder for makepkg remains.
The act_runner now uses docker mode with archlinux:base-devel. Install git/curl and create a builder user since makepkg refuses to run as root.
Triggers on PKGBUILD changes (from pkgver-bot commits). Builds the changed package with makepkg and uploads the .pkg.tar.zst to the Gitea Arch Package Registry.
