Git commits in Moodle 3.6.9 by Marina Glancy

commit e972cd3ef380b09149424eba3cb6c41b9a8de0a4
Author: Marina Glancy <marina@moodle.com>
Date:   Wed, 04 Mar 2020 01:30:06 +0800
Tag:    v3.6.9

MDL-56287 gradereport_history: Separate groups queries improved