$ git clone -n https://src.fedoraproject.org/rpms/cmatrix.git /var/lib/mock/f45-build-4062-330/root/chroot_tmpdir/scmroot/cmatrix
Cloning into '/var/lib/mock/f45-build-4062-330/root/chroot_tmpdir/scmroot/cmatrix'...
$ git fetch origin e4b063f6c30632f6e389b173a816a33923ca9d7d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/cmatrix
 * [new ref]         e4b063f6c30632f6e389b173a816a33923ca9d7d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e4b063f Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild