Merge branch 'security-390910-15-10' into '15-10-stable-ee'

Prohibit 40 character hex sets at beginning of path-based branch name

See merge request https://gitlab.com/gitlab-org/security/gitlab/-/merge_requests/3194



Merged-by: GitLab Release Tools Bot <delivery-team+release-tools@gitlab.com>
Approved-by: Vasilii Iakliushin <viakliushin@gitlab.com>
Co-authored-by: Robert May <rmay@gitlab.com>