Add unique indexes to ci_job_artifacts

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138620



Merged-by: Eulyeon Ko <5961404-euko@users.noreply.gitlab.com>
Approved-by: Dmitry Gruzd <dgruzd@gitlab.com>
Approved-by: Eulyeon Ko <5961404-euko@users.noreply.gitlab.com>
Reviewed-by: Dmitry Gruzd <dgruzd@gitlab.com>
Reviewed-by: Eulyeon Ko <5961404-euko@users.noreply.gitlab.com>
Co-authored-by: Maxime Orefice <morefice@gitlab.com>