Deferred feedback with explicit validation - Moodle 5.1 support

[acquaalta]

Hi,
Could you please update the plugin (qbehaviour_dfexplicitvaildate) so it would officially support Moodle 5.1?

Thanks 🙏

[sangwinc]

Thanks for the nudge @acquaalta. Yes, these additional behviour plugins have all been tested on 5.0 and 5.1. I've updated the moodle plugin DB accordingly.