Author: Eloy Lafuente (stronk7)
MDL-63421 env: Moodle 3.4.x and 3.5.x do not support PHP 7.3
http://git.moodle.org/gw?p=moodle.git;a=commit;h=9dfe3e0be197dca222d5bcb7c4d369ddcb181218
http://github.com/moodle/moodle/commit/9dfe3e0be197dca222d5bcb7c4d369ddcb181218
+ 3.1 en [unsupportedphpversion73,core_admin]