$ git clone -n https://src.fedoraproject.org/rpms/rubygem-gem2rpm.git /var/lib/mock/f41-build-side-1-2849151-33909/root/chroot_tmpdir/scmroot/rubygem-gem2rpm
Cloning into '/var/lib/mock/f41-build-side-1-2849151-33909/root/chroot_tmpdir/scmroot/rubygem-gem2rpm'...
$ git fetch origin b9e70863e795a7c22487ac1a441599cc1fd9b944:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-gem2rpm
 * [new ref]         b9e70863e795a7c22487ac1a441599cc1fd9b944 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b9e7086 convert GPLv2+ license to SPDX