$ git clone -n https://src.fedoraproject.org/rpms/diffoscope.git /var/lib/mock/f40-build-2539039-61857/root/chroot_tmpdir/scmroot/diffoscope
Cloning into '/var/lib/mock/f40-build-2539039-61857/root/chroot_tmpdir/scmroot/diffoscope'...
$ git fetch origin 990d6cf1b3598afac7388bd9289c8c2407d5981c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/diffoscope
 * [new ref]         990d6cf1b3598afac7388bd9289c8c2407d5981c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 990d6cf Version 260