$ git clone -n https://src.fedoraproject.org/rpms/build2.git /var/lib/mock/f40-build-1992064-43552/root/chroot_tmpdir/scmroot/build2
Cloning into '/var/lib/mock/f40-build-1992064-43552/root/chroot_tmpdir/scmroot/build2'...
$ git fetch origin 23cf0d66a49ab6528a3df0640ebc9d5b332187d3:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/build2
 * [new ref]         23cf0d66a49ab6528a3df0640ebc9d5b332187d3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 23cf0d6 Update to v0.16.0