[IMP] stock: add empty group in production lot form view

Currently stock.production.lot form view doesn't propose a second
column by default and the "column" component won't work from studio.
(It works well when no column exist, but not when one already exists)

So added an empty group for consistent studio customization in the
stock.production.lot form view.

closes odoo/odoo#47794

Taskid: 2043928
Closes: #47794
Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>

addons/stock/views/stock_production_lot_views.xml

@@ -30,6 +30,7 @@
                         <field name="ref"/>
                         <field name="company_id" groups="base.group_multi_company"/>
                     </group>
+                    <group></group>
                 </group>
                 <notebook attrs="{'invisible': [('display_complete', '=', False)]}">
                     <page string="Description" name="description">