Use grouped attribute on message.xml

issue8556
review272001002

message.xml

@@ -2,7 +2,7 @@
 <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
 this repository contains the full copyright notices and license terms. -->
 <tryton>
-    <data group="1">
+    <data grouped="1">
         <record model="ir.message" id="msg_party_credit_limit_amount">
             <field name="text">Party "%(party)s" has reached their credit limit of %(limit)s.</field>
         </record>