$ git clone -n https://src.fedoraproject.org/rpms/rubygem-racc.git /var/lib/mock/f45-build-35228-694/root/chroot_tmpdir/scmroot/rubygem-racc
Cloning into '/var/lib/mock/f45-build-35228-694/root/chroot_tmpdir/scmroot/rubygem-racc'...
$ git fetch origin dc04b63d0969fb96d03ba221988650a3190be15f:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-racc
 * [new ref]         dc04b63d0969fb96d03ba221988650a3190be15f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at dc04b63 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild