[IMP] account_payment_order: make reference_type modifiable on posted…

… invoice

The Odoo payment_reference field is modifiable, so the reference type
should be modifiable too.

account_payment_order/views/account_invoice_view.xml

@@ -61,8 +61,7 @@
             <field name="payment_reference" position="before">
                 <field
                     name="reference_type"
-                    attrs="{'readonly':[('state','!=','draft')],
-                            'invisible': [('move_type', 'not in', ('out_invoice', 'out_refund'))],
+                    attrs="{'invisible': [('move_type', 'not in', ('out_invoice', 'out_refund'))],
                             'required': [('move_type', 'in', ('out_invoice', 'out_refund'))]}"
                 />
             </field>