$ git clone -n https://src.fedoraproject.org/rpms/rubygem-mustermann.git /var/lib/mock/f45-build-35048-693/root/chroot_tmpdir/scmroot/rubygem-mustermann
Cloning into '/var/lib/mock/f45-build-35048-693/root/chroot_tmpdir/scmroot/rubygem-mustermann'...
$ git fetch origin f51d8dc46f92dd249192ce66ac2e9006e5cc2d2a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-mustermann
 * [new ref]         f51d8dc46f92dd249192ce66ac2e9006e5cc2d2a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f51d8dc Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild