Git merges in Moodle 3.9.x by AMOS bot

commit 31d0ccb07867baba0d7e2fe380390692f2b50bf5
Author: AMOS bot <amos@moodle.org>
Date:   Sat, 12 Dec 2020 08:07:54 +0800
Tag:    v3.9.4

Merge branch 'MOODLE_39_STABLE' into install_39_STABLE