$ git clone -n https://src.fedoraproject.org/rpms/rubygem-json.git /var/lib/mock/f45-build-35059-693/root/chroot_tmpdir/scmroot/rubygem-json
Cloning into '/var/lib/mock/f45-build-35059-693/root/chroot_tmpdir/scmroot/rubygem-json'...
$ git fetch origin d066dcf06dbd879ebbb6da46bbe038919aa1d26b:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-json
 * [new ref]         d066dcf06dbd879ebbb6da46bbe038919aa1d26b -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at d066dcf 2.21.2