fix: use type='html' not type='qweb' for mail template body_html

type='qweb' is not a valid value in Odoo's data-file RNG schema (allowed:
char/int/float/html/xml/file/base64/ref). It caused a misleading
"Element odoo has extra content: data" validation error that aborted the
entire module upgrade. type='html' with t-out/t-foreach/t-if directives
as real XML children is the correct Odoo 17 pattern; body_html renders
with the qweb engine at send time regardless.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

addons/itsulu_blog_publisher/data/mail_template_data.xml

@@ -8,7 +8,7 @@
             <field name="subject">[ITSulu Insights] Blog Post Published: {{ object.blog_post_id.name }}</field>
             <field name="email_from">{{ user.email_formatted }}</field>
             <field name="auto_delete">True</field>
-            <field name="body_html" type="qweb"><![CDATA[
+            <field name="body_html" type="html">
                 <div style="font-family: Arial, sans-serif; line-height: 1.6; max-width: 700px;">
                     <h2>Blog Post Published</h2>
                     <p><strong>Title:</strong> <t t-out="object.blog_post_id.name"/></p>
@@ -42,7 +42,7 @@
                         </t>
                     </t>
                 </div>
-            ]]></field>
+            </field>
         </record>
 
     </data>