$ git clone -n https://src.fedoraproject.org/rpms/gtkmm4.0.git /var/lib/mock/f41-build-842792-161713/root/chroot_tmpdir/scmroot/gtkmm4.0
Cloning into '/var/lib/mock/f41-build-842792-161713/root/chroot_tmpdir/scmroot/gtkmm4.0'...
$ git fetch origin 068e19d32931d1275213a4a6d5a03b9d8933e294:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gtkmm4.0
 * [new ref]         068e19d32931d1275213a4a6d5a03b9d8933e294 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 068e19d Update to 4.15.0