www/gitlab: security and patch update to 18.6.1

Changes: https://about.gitlab.com/releases/2025/11/26/patch-release-gitlab-18-6-1-released/
Security: 4530fc9f-cb47-11f0-85d8-2cf05da270f3
(cherry picked from commit 870130e039ac160ad9fff72b1b4c87f01b0735ff)