$ git clone -n https://src.fedoraproject.org/rpms/rubygem-json_spec.git /var/lib/mock/f45-build-35065-693/root/chroot_tmpdir/scmroot/rubygem-json_spec
Cloning into '/var/lib/mock/f45-build-35065-693/root/chroot_tmpdir/scmroot/rubygem-json_spec'...
$ git fetch origin 74302824d99fd6ff968bb62f6be815afeb912de0:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-json_spec
 * [new ref]         74302824d99fd6ff968bb62f6be815afeb912de0 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 7430282 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild