[FIX] website_sale: shop search with collapsible hierarchy

When the eCommerce /shop page was configured to use collapsible product
categories, performing a search on a product whose eCommerce category
was a child of another one produced an error.

This was due to a typo made with https://github.com/odoo/odoo/commit/8889d00f4f702bb22416b0751b46dac28411d46d

Closes https://github.com/odoo/odoo/issues/28435

closes odoo/odoo#28532

addons/website_sale/views/templates.xml

@@ -323,7 +323,7 @@
             <a t-att-href="keep('/shop/category/' + slug(categ), category=0)" t-attf-class="nav-link#{' active' if categ.id == int(category or 0) else ''}" t-field="categ.name"></a>
             <ul t-if="categ.child_id" class="nav nav-pills flex-column nav-hierarchy" t-att-style="'display:block;' if categ.id in parent_category_ids else 'display:none;'">
                 <t t-foreach="categ.child_id" t-as="categ">
-                    <t t-if="not search or c.id in search_categories_ids">
+                    <t t-if="not search or categ.id in search_categories_ids">
                         <t t-call="website_sale.option_collapse_categories_recursive" />
                     </t>
                 </t>