[FIX] web : Stages positioned properly when there is no sheet

- Task: https://www.odoo.com/web#id=8942&view_type=form&model=project.task&action=333&active_id=131
- Pad: https://pad.odoo.com/p/r.KfYk8Is3m7EnW2U4
You are applying same css as ".openerp .oe_form > :not(.oe_form_nosheet) header ul" then why not keep comma separated selector ?