Git commits in Moodle 3.9.4 by John Yao

commit 78aeaf17e7cd7080d307a8774fec858e913cb344
Author: John Yao <johnyao@catalyst-au.net>
Date:   Thu, 19 Nov 2020 09:36:32 +0800
Tag:    v3.9.4

MDL-67636 gradebook: Prevent exposing hidden grade in locked category