www/gitlab: security and patch update to 18.6.2
Changes: https://about.gitlab.com/releases/2025/12/10/patch-release-gitlab-18-6-2-released/
Security: c6c9306e-d645-11f0-8ce2-2cf05da270f3
(cherry picked from commit 23953a07624c5925406d169990095885d3ede897)