$ git clone -n https://src.fedoraproject.org/rpms/perl-Mail-Box.git /var/lib/mock/f45-build-53457-923/root/chroot_tmpdir/scmroot/perl-Mail-Box
Cloning into '/var/lib/mock/f45-build-53457-923/root/chroot_tmpdir/scmroot/perl-Mail-Box'...
$ git fetch origin 7ca2a511a97b08e127a654602c620b3e5f88e7f4:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/perl-Mail-Box
 * [new ref]         7ca2a511a97b08e127a654602c620b3e5f88e7f4 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 7ca2a51 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild