$ git clone -n https://src.fedoraproject.org/rpms/gtkmm2.4.git /var/lib/mock/f45-build-13167-447/root/chroot_tmpdir/scmroot/gtkmm2.4
Cloning into '/var/lib/mock/f45-build-13167-447/root/chroot_tmpdir/scmroot/gtkmm2.4'...
$ git fetch origin 53f9a999482c32893a874c5bf7c786ff761b5d94:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gtkmm2.4
 * [new ref]         53f9a999482c32893a874c5bf7c786ff761b5d94 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 53f9a99 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild