Git commits in Moodle 3.9.0 by Marcus Boon

commit f1f5ba36ad7893e3fcc98a54804e1dbd22c3bea8
Author: Marcus Boon <marcus@catalyst-au.net>
Date:   Thu, 09 Apr 2020 11:00:29 +0800
Tag:    v3.9.0-beta

MDL-68388 core_grades: Use MUC for grade letters