[FIX] website_sale: sale ribbon not saving

Current behaviour:
When editing a product, try to add a ribbon,
it will not save.

Steps to reproduce:
1. Go to website
2. Go to Shop
3. Click on Edit (top right)
4. Select any product
5. At Badge: Select Sale
6. (badge is visible)
7. Click on Save
8. (badge is gone)

Cause of the issue:
The element was not considered "dirty"

opw-3487397

closes odoo/odoo#135351

X-original-commit: 5d13fa522e7d06b03a098ada5fa6be15ddc49618
Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>
Signed-off-by: Antoine Demany (ande) <ande@odoo.com>

addons/website_sale/views/templates.xml

@@ -175,7 +175,7 @@
                     <t t-set="bg_color" t-value="td_product['ribbon']['bg_color'] or ''"/>
                     <t t-set="text_color" t-value="td_product['ribbon']['text_color']"/>
                     <t t-set="bg_class" t-value="td_product['ribbon']['html_class']"/>
-                    <span t-attf-class="o_ribbon #{bg_class}" t-attf-style="#{text_color and ('color: %s; ' % text_color)}#{bg_color and 'background-color:' + bg_color}" t-out="td_product['ribbon']['html'] or ''"/>
+                    <span t-attf-class="o_ribbon #{bg_class}" t-attf-style="#{text_color and ('color: %s; ' % text_color)}#{bg_color and 'background-color:' + bg_color}" t-field="product.website_ribbon_id.html"/>
                 </a>
             </div>
             <div class="o_wsale_product_information position-relative d-flex flex-column flex-grow-1 flex-shrink-1">