$ git clone -n https://src.fedoraproject.org/rpms/R-processx.git /var/lib/mock/f43-build-side-110352-58908265-6569187/root/chroot_tmpdir/scmroot/R-processx
Cloning into '/var/lib/mock/f43-build-side-110352-58908265-6569187/root/chroot_tmpdir/scmroot/R-processx'...
$ git fetch origin 750a989e11d28ea7613e8eaf372e4bca7491695a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-processx
 * [new ref]         750a989e11d28ea7613e8eaf372e4bca7491695a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 750a989 R-maint-sig mass rebuild