$ git clone -n https://src.fedoraproject.org/rpms/blackbox.git /var/lib/mock/f40-build-747447-113175/root/chroot_tmpdir/scmroot/blackbox
Cloning into '/var/lib/mock/f40-build-747447-113175/root/chroot_tmpdir/scmroot/blackbox'...
$ git fetch origin a67679639c1d4fca958a2f3fa5ad3e9433755cd9:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/blackbox
 * [new ref]         a67679639c1d4fca958a2f3fa5ad3e9433755cd9 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a676796 opt-in to autochangelog