[FIX] digest, mass_mailing: correctly set body before odoo mentions

Body is used in statistics as an additional content to digest layout. However
it is strangely located after Odoo mentions (Send by, ...). Currently link
trackers statistics are therefore at the end of the email. They belong to
the "core" section of the emails.

Task-2686586 (Repair mailing statistics email)

Part-of: odoo/odoo#79653

addons/digest/data/digest_data.xml

@@ -391,6 +391,8 @@
     </div>
 </div>
 
+<t t-if="body" t-out="body"/>
+
 <div>
     <div class="global_layout">
         <div class="preference_div">
@@ -412,7 +414,6 @@
     </div>
 </div>
 
-<t t-if="body" t-out="body"/>
 <div t-if="display_mobile_banner" t-call="digest.digest_section_mobile" />
 
 <div class="global_layout" id="footer">