xfce-build: Always pick the latest stable release

Alternatively we could also pick the latest overall release, but the
downside would be that the container could jump back and forth between
4.17 dev and 4.16 maintenance releases.
git describe --tags `git rev-list --tags --max-count=1` --match "$NAME*"
3 jobs for !49 with fix-pulling-tags in 11 minutes and 6 seconds (queued for 3 seconds)
latest merge request