$ git clone -n https://github.com/xcp-ng-rpms/kernel.git /var/lib/mock/v8.3-u-prebuild-9266-28049/root/chroot_tmpdir/scmroot/kernel
Cloning into '/var/lib/mock/v8.3-u-prebuild-9266-28049/root/chroot_tmpdir/scmroot/kernel'...
$ git fetch origin a91aa4a4126259f79003fe920a9d3e2475b61750:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/kernel
 * [new ref]             a91aa4a4126259f79003fe920a9d3e2475b61750 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a91aa4a41 bump release for test build