Use Alpine Stable for CI

Currently, we're using Alpine Edge for the CI here in pmaports. This can be a problem whenever there is some form of disruption on Edge as it can result in our CI malfunctioning which prevents us from merging.

The only missing component is Ruff, which isn't available in Alpine 3.19. However, it will be available in Alpine 3.20 as it was moved to community during this release cycle: https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/62711. As such, once Alpine 3.20 releases, we should move over to using Alpine Stable for the CI.