Bump `mini_magick` to 4.12

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/146883



Merged-by: Dmitry Gruzd <dgruzd@gitlab.com>
Approved-by: Hinam Mehra <hmehra@gitlab.com>
Approved-by: Dmitry Gruzd <dgruzd@gitlab.com>
Reviewed-by: Dmitry Gruzd <dgruzd@gitlab.com>
Reviewed-by: Bojan Marjanovic <bmarjanovic@gitlab.com>
Co-authored-by: bmarjanovic <bmarjanovic@gitlab.com>