Git commits in Moodle 3.7.5 by Mark Johnson

commit e5ec4988b63f57639fa563f9ac4a919d04fad299
Author: Mark Johnson <mark.johnson@open.ac.uk>
Date:   Mon, 13 Jan 2020 19:37:09 +0800
Tag:    v3.7.5

MDL-67674 Cache: Lock rebuilding of the course category tree cache