$ git clone -n https://src.fedoraproject.org/rpms/rubygem-actionmailbox.git /var/lib/mock/f39-build-1595037-38323/root/chroot_tmpdir/scmroot/rubygem-actionmailbox
Cloning into '/var/lib/mock/f39-build-1595037-38323/root/chroot_tmpdir/scmroot/rubygem-actionmailbox'...
$ git fetch origin cea411b8712e56ad8d6c9acf50fa11a25fad09a8:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-actionmailbox
 * [new ref]         cea411b8712e56ad8d6c9acf50fa11a25fad09a8 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cea411b Update to actionmailbox 7.0.8