Add suffix for completion rules on Moodle 4.3+

[izendegi]

From version 4.3 Moodle needs to append a suffix to completion rules (https://moodledev.io/docs/4.3/devupdate#append-a-suffix-to-the-completion-rules).

Missing these results in being removed from the Default activity completion form.

Doing something similar to this should be enough to fix this.

[danmarsden]

Thanks for the report - feel free to help further by submitting a pull request otherwise we'll try to get to this sometime!