Update dependency prometheus-client-mmap to '~> 0.28'

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/130788



Merged-by: Stan Hu <stanhu@gmail.com>
Approved-by: Will Chandler <wchandler@gitlab.com>
Approved-by: Stan Hu <stanhu@gmail.com>
Co-authored-by: GitLab Renovate Bot <gitlab-bot@gitlab.com>