[FIX] website: properly align checkboxes in website forms

With [1], checkboxes in website forms were wrapped in a <div/> with the
"form-check" bootstrap class (as they should). That forgot to mark the
checkboxes themselves with the class "form-check-input". Without it they
are misaligned.

This fixes the error for newly added checkboxes in forms. Old ones will
stay "broken".

[1]: https://github.com/odoo/odoo/commit/9ea276ae2f00c3a5ba4e10af313085947e70e265

Related to opw-3003952

Part-of: odoo/odoo#105870

addons/website/static/src/xml/website_form_editor.xml

@@ -240,7 +240,7 @@
                 <input
                     type="checkbox"
                     value="Yes"
-                    class="s_website_form_input"
+                    class="s_website_form_input form-check-input"
                     t-att-name="field.name"
                     t-att-checked="field.value and 'checked' or None"
                     t-att-required="field.required || field.modelRequired || None"