Copy Up: drop 'at least' from the security=4 ReleaseNotes.adoc
wording, from dev@33492. Regenerated ReleaseNotes.{html,pdf}.
This was the only content still pending Copy Up from dev to main
(found while checking the push_bins.sh Copy Up candidates earlier
today); main's upgrade.sh already had this wording fix via a
separate earlier Copy Up, but ReleaseNotes.adoc/.html/.pdf did not.