$ git clone -n https://src.fedoraproject.org/rpms/gtkmm3.0.git /var/lib/mock/f45-build-13190-447/root/chroot_tmpdir/scmroot/gtkmm3.0
Cloning into '/var/lib/mock/f45-build-13190-447/root/chroot_tmpdir/scmroot/gtkmm3.0'...
$ git fetch origin 5a4651f2854d7d7df7d79004e41217421edde98b:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gtkmm3.0
 * [new ref]         5a4651f2854d7d7df7d79004e41217421edde98b -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5a4651f Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild