$ git clone -n https://src.fedoraproject.org/rpms/nginx.git /var/lib/mock/f43-build-60971131-6587132/root/chroot_tmpdir/scmroot/nginx
Cloning into '/var/lib/mock/f43-build-60971131-6587132/root/chroot_tmpdir/scmroot/nginx'...
$ git fetch origin b3a8e1bdcf9816732a749a5c0b237c36d8ab74d3:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/nginx
 * [new ref]         b3a8e1bdcf9816732a749a5c0b237c36d8ab74d3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b3a8e1b update to 1.28.0