[FIX] purchase_requisition: No drag and drop when grouped by state

Before this commit, it was possible to change the state of the Purchase Agreement when Grouped by `state` on Kanban view which is not Ideal Behavior.

Now we block drag and drop when grouping by State.

closes odoo/odoo#44674

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

addons/purchase_requisition/views/purchase_requisition_views.xml

@@ -234,7 +234,7 @@
                                 <div class="o_kanban_record_headings mt4">
                                     <strong class="o_kanban_record_title"><span><field name="name"/></span></strong>
                                 </div>
-                                <field name="state" widget="label_selection" options="{'classes': {'draft': 'default', 'in_progress': 'default', 'open': 'success', 'done': 'success', 'close': 'danger'}}"/>
+                                <field name="state" widget="label_selection" options="{'classes': {'draft': 'default', 'in_progress': 'default', 'open': 'success', 'done': 'success', 'close': 'danger'}}" readonly="1" />
                             </div>
                             <div class="o_kanban_record_body">
                                 <span class="text-muted"><field name="type_id"/></span>