[ADD,IMP]Website_forum:Add a python test case

- Task: https://www.odoo.com/web#id=8745&view_type=form&model=project.task&menu_id=3942&action=327
- Pad: https://pad.odoo.com/p/r.EsLOcZQQuvZYB4ll
That's completely useless:

1. res is already a promise
2. AFAIK the only return value from event handlers jQuery cares for is `false`, which is a shortcut for `ev.stopPropagation(); ev.preventDefault();`