$ git clone -n https://src.fedoraproject.org/rpms/glibmm2.68.git /var/lib/mock/f39-build-1501485-34843/root/chroot_tmpdir/scmroot/glibmm2.68
Cloning into '/var/lib/mock/f39-build-1501485-34843/root/chroot_tmpdir/scmroot/glibmm2.68'...
$ git fetch origin 08127ebd1ba9b065482b935c66338ce0f191d86d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/glibmm2.68
 * [new ref]         08127ebd1ba9b065482b935c66338ce0f191d86d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 08127eb Update to 2.78.0