[FIX] mrp: change production graph view

The mrp_production graph view group records by date_deadline. This
date is optionnal so the graph view could missed some records if the date
is empty.
This commit change it by a required one (date_planned_finished) in order
to display all productions

closes odoo/odoo#36939

Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>

addons/mrp/views/mrp_production_views.xml

@@ -286,7 +286,7 @@
             <field name="model">mrp.production</field>
             <field name="arch" type="xml">
                 <graph string="Manufacturing Orders" type="line">
-                    <field name="date_deadline"/>
+                    <field name="date_planned_finished"/>
                 </graph>
             </field>
         </record>