$ git clone -n https://src.fedoraproject.org/rpms/polymake.git /var/lib/mock/f40-build-782783-132277/root/chroot_tmpdir/scmroot/polymake
Cloning into '/var/lib/mock/f40-build-782783-132277/root/chroot_tmpdir/scmroot/polymake'...
$ git fetch origin 66e5d3d2e7c1377993015ae60590520db0e8ef44:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/polymake
 * [new ref]         66e5d3d2e7c1377993015ae60590520db0e8ef44 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 66e5d3d Adjust sed expressions to fix FTBFS