Don't force Alpine's version to 'latest'

It seems that Alpine images are forced to use the version 'latest': https://gitlab.freedesktop.org/freedesktop/ci-templates/-/blob/master/templates/alpine.yml?ref_type=heads#L8

Would it be possible to select other versions? Although using 'latest' is the most common, Alpine's released versions are supported for 2+ years: https://alpinelinux.org/releases/. We are interested in testing the correct version of Alpine that ships each stable version of NetworkManager.