[FIX] website: await async part when changing transparent header color

Commit [1] adapted the topMenuColor option to the 14.0 editor but
did not await the call to action_demand.

This didn't cause any issue but could lead to race conditions and is
not correct.

It also breaks after [2].

[1]: https://github.com/odoo/odoo/commit/98c8438f5225dbc34b15fc2ed5b9918d537bb71b
[2]: https://github.com/odoo/odoo/commit/31cc10b91dc7762e23b4bde9b945be0c4ce3fe3b

task-2687506

closes odoo/odoo#96059

X-original-commit: a22afd698e7c04d302a1c90888b015413dd8c930
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>
Signed-off-by: Arthur Detroux (ard) <ard@odoo.com>

addons/website/static/src/js/editor/snippets.options.js

@@ -2239,12 +2239,16 @@ options.registry.topMenuColor = options.Class.extend({
     /**
      * @override
      */
-    selectStyle(previewMode, widgetValue, params) {
-        this._super(...arguments);
+    async selectStyle(previewMode, widgetValue, params) {
+        await this._super(...arguments);
         const className = widgetValue ? (params.colorPrefix + widgetValue) : '';
-        this.trigger_up('action_demand', {
-            actionName: 'toggle_page_option',
-            params: [{name: 'header_color', value: className}],
+        await new Promise((resolve, reject) => {
+            this.trigger_up('action_demand', {
+                actionName: 'toggle_page_option',
+                params: [{name: 'header_color', value: className}],
+                onSuccess: resolve,
+                onFailure: reject,
+            });
         });
     },