[FIX] portal: VAT modification

The route `/my/account` doesn't implement any restriction for the VAT
modification. This allows users to modify the VAT number although they
shouldn't.

We make the restriction consistent with the backend:

https://github.com/odoo/odoo/blob/e0c7a368580dfeac9af8dc3cb3a10fc33bf4b521/odoo/addons/base/res/res_partner_view.xml#L247

opw-2056727

closes odoo/odoo#36031

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/portal/views/portal_templates.xml

@@ -279,7 +279,8 @@
                             </div>
                             <div t-if="has_check_vat" t-attf-class="form-group #{error.get('vat') and 'has-error' or ''} col-lg-6">
                                 <label class="control-label label-optional" for="vat">VAT Number</label>
-                                <input type="text" name="vat" class="form-control" t-att-value="vat or partner.vat" />
+                                <!-- DO NOT FORWARD-PORT! ONLY FOR v11 -->
+                                <input type="text" name="vat" class="form-control" t-att-value="vat or partner.vat" t-att-readonly="'1' if partner.parent_id else None" />
                             </div>
 
                             <div class="clearfix" />