$ git clone -n https://src.fedoraproject.org/rpms/mozilla-ublock-origin.git /var/lib/mock/f39-build-1677209-40958/root/chroot_tmpdir/scmroot/mozilla-ublock-origin
Cloning into '/var/lib/mock/f39-build-1677209-40958/root/chroot_tmpdir/scmroot/mozilla-ublock-origin'...
$ git fetch origin 3a9433ffd030d8cc062ac3e0a2693a48a2fd96bd:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mozilla-ublock-origin
 * [new ref]         3a9433ffd030d8cc062ac3e0a2693a48a2fd96bd -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3a9433f Merge branch 'f38' into f39