$ git clone -n https://github.com/xcp-ng-rpms/gmp /var/lib/mock/v8.3-u-pcoval2-10911-29400/root/chroot_tmpdir/scmroot/gmp
Cloning into '/var/lib/mock/v8.3-u-pcoval2-10911-29400/root/chroot_tmpdir/scmroot/gmp'...
$ git fetch origin ded7d8e522b0191cac20e5439bf0f902701e9b2b:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/gmp
 * [new ref]         ded7d8e522b0191cac20e5439bf0f902701e9b2b -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ded7d8e bump release for test build