$ git clone -n https://src.fedoraproject.org/rpms/python-zbase32.git /var/lib/mock/f40-build-2247304-53867/root/chroot_tmpdir/scmroot/python-zbase32
Cloning into '/var/lib/mock/f40-build-2247304-53867/root/chroot_tmpdir/scmroot/python-zbase32'...
$ git fetch origin 7ad748d902b220671f982834e9b645dd8f4e73fe:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/python-zbase32
 * [new ref]         7ad748d902b220671f982834e9b645dd8f4e73fe -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 7ad748d Drop a forgotten bootstrap switch -- this will now FTBFS as it should