www/gitlab: major upgrade to 16.11.0

Please note, that this version changes the installation path.
Make sure you follow the upgrade manual very carefully:
https://gitlab.fechner.net/mfechner/Gitlab-docu/-/blob/master/update/16.10-16.11-freebsd.md

Changes: https://about.gitlab.com/releases/2024/04/18/gitlab-16-11-released/