Merge branch 'hly-fix-mail-smtp-pool' into 'master'

Upgrade bundler version in mail-smtp_pool

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/169559



Merged-by: Matthias Käppler <mkaeppler@gitlab.com>
Approved-by: Matthias Käppler <mkaeppler@gitlab.com>
Approved-by: Kev Kloss <kkloss@gitlab.com>
Co-authored-by: Heinrich Lee Yu <heinrich@gitlab.com>