[FIX] website: permit to save when two TOC are on the same page

Since [this commit], when dropping several "table of content" blocks on
the same page, it was impossible to save. This commit solves this
problem.
Steps to reproduce the resolved bug:
- In edit mode, drop two TOC blocks
- Click on Save

=> the UI is blocked

[this commit]: https://github.com/odoo/odoo/commit/06b03ba5ef8375b1236f6ecb52ac468124e910ba

Related to opw-3047375
Related to opw-3035502
task-2948895

X-original-commit: a6de596017cdbd0da10b4050da132d46dc82a491
Part-of: odoo/odoo#107732

addons/website/static/src/snippets/s_table_of_content/000.js

@@ -25,7 +25,10 @@ const TableOfContent = publicWidget.Widget.extend({
         if (indexCallback >= 0) {
             extraMenuUpdateCallbacks.splice(indexCallback, 1);
         }
-        this._scrollingElement.scrollspy('dispose');
+        const scrollSpyInstance = ScrollSpy.getInstance(this._scrollingElement);
+        if (scrollSpyInstance) {
+            scrollSpyInstance.dispose();
+        }
         this.$el.css('top', '');
         this.$el.find('.s_table_of_content_navbar').css('top', '');
         this._super(...arguments);

addons/website/static/tests/tours/snippet_table_of_content.js

@@ -0,0 +1,15 @@
+/** @odoo-module */
+
+import wTourUtils from 'website.tour_utils';
+
+wTourUtils.registerWebsitePreviewTour('snippet_table_of_content', {
+    test: true,
+    url: '/',
+    edition: true,
+}, [
+    wTourUtils.dragNDrop({id: 's_table_of_content', name: 'Table of Content'}),
+    wTourUtils.dragNDrop({id: 's_table_of_content', name: 'Table of Content'}),
+    // To make sure that the public widgets of the two previous ones started.
+    wTourUtils.dragNDrop({id: 's_banner', name: 'Banner'}),
+    ...wTourUtils.clickOnSave(),
+]);

addons/website/tests/test_snippets.py

@@ -49,3 +49,6 @@ class TestSnippets(HttpCase):
 
     def test_07_image_gallery(self):
         self.start_tour(self.env['website'].get_client_action_url('/'), 'snippet_image_gallery', login='admin')
+
+    def test_08_table_of_content(self):
+        self.start_tour(self.env['website'].get_client_action_url('/'), 'snippet_table_of_content', login='admin')