Git commits in Moodle 3.9.6 by Brendan Heywood

commit 23cc13e8ef2b9123f5320b223fcde71a9a4643b4
Author: Brendan Heywood <brendan@catalyst-au.net>
Date:   Wed, 17 Mar 2021 14:37:29 +0800
Tag:    v3.9.6

MDL-71068 login: Fix edge cases with $CFG->protectusernames