$CFG->scheduled_tasks has incorrect order for dayofweek and months in cron spec

$CFG->scheduled_tasks can define a forced cron spec, but this spec has a typo in it which swaps the dayofweek and month fields:

https://github.com/moodle/moodle/blob/master/config-dist.php#L1132

This was not intentional and the cron spec should just be the standard with month first then dayofweek:

https://en.wikipedia.org/wiki/Cron#CRON_expression