[FIX] theme_test_custo: prevent failing test_website_theme_preview tour

When running the test test_website_theme_preview, we have the following error:

`tour.steps has to be a function that returns TourStep[]`

runbot-111646
runbot-163139

closes odoo/design-themes#1062

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

theme_test_custo/static/tests/tours/website_theme_preview.js

@@ -5,8 +5,8 @@ import { registry } from "@web/core/registry";
 registry.category("web_tour.tours").add("website_theme_preview", {
     test: true,
     url: "/web#action=website.action_website_configuration",
-},
-[{
+    steps: () => [
+{
     content: "Click on create new website",
     trigger: 'button[name="action_website_create_new"]',
 }, {
@@ -38,4 +38,4 @@ registry.category("web_tour.tours").add("website_theme_preview", {
     content: "Check that the desktop view is active",
     trigger: ".o_view_form_theme_preview_controller .o_field_iframe > div:not(.is_mobile):visible",
     run: () => null, // it's a check
-}]);
+}]});