$ git clone -n https://src.fedoraproject.org/rpms/golang-github-prometheus.git /var/lib/mock/f40-build-781849-131884/root/chroot_tmpdir/scmroot/golang-github-prometheus
Cloning into '/var/lib/mock/f40-build-781849-131884/root/chroot_tmpdir/scmroot/golang-github-prometheus'...
$ git fetch origin 3d92312e6a9fdfede84dfeafa0ade88a12558354:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/golang-github-prometheus
 * [new ref]         3d92312e6a9fdfede84dfeafa0ade88a12558354 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3d92312 Rebuild to fix FTBFS