$ git clone -n https://src.fedoraproject.org/rpms/vtk.git /var/lib/mock/f40-build-1768790-24748/root/chroot_tmpdir/scmroot/vtk
Cloning into '/var/lib/mock/f40-build-1768790-24748/root/chroot_tmpdir/scmroot/vtk'...
$ git fetch origin 3300be518ba7bb4dd6531fd059b99ae1685ea8ec:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/vtk
 * [new ref]         3300be518ba7bb4dd6531fd059b99ae1685ea8ec -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3300be5 Set Java source/target version to 8 (FTBFS bz#2272954)