[FIX] website: add the necessary field in the kanban view

Before this commit,
The 'icon' field is referenced in the link below
https://github.com/odoo/odoo/blob/d8315df6fd733c1331911583f86803bad1718d2d/addons/website/views/website_views.xml#L444
But it has not been defined on the kanban view
(Actually it has been removed from the view by this commit: https://github.com/odoo/odoo/commit/69b24e4de17878ea5bc5f3509f0c9aa7c06be20a)
And because of this, below error is thrown:
TypeError: Cannot read properties of undefined (reading 'value')
while clicking the 'Pick a theme' button in Website settings.

After this commit,
This issue has been resolved.

closes odoo/odoo#81578

closes odoo/odoo#82204

X-original-commit: 5c67cac537082698e0cf6d1d82167c96402f6cf3
Signed-off-by: Romain Derie (rde) <rde@odoo.com>

addons/website/views/website_views.xml

@@ -429,6 +429,7 @@
             <field name="model">ir.module.module</field>
             <field name="arch" type="xml">
                 <kanban create="false" class="o_theme_kanban" default_order="state,sequence,name" js_class="theme_preview_kanban">
+                    <field name="icon"/>
                     <field name="summary"/>
                     <field name="name"/>
                     <field name="state"/>