[IMP] purchase : Improve purchase module views - BST onboarding

https://www.odoo.com/web#id=10537&view_type=form&model=project.task&menu_id=3942&action=327
pad: https://pad.odoo.com/p/r.0g7NjI7wwVRcZBem
You don't have to cast the domain in a string.
`res['domain] = [('id', 'in', inv_ids)]` should be fine.