[FIX] website: prevent scroll button editing

Before this commit, it was possible to edit scroll buttons with the
editor toolbar.

task-2656662

closes odoo/odoo#78532

Related: odoo/design-themes#518
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

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

@@ -2574,6 +2574,7 @@ options.registry.ScrollButton = options.Class.extend({
                     'justify-content-center',
                     'mx-auto',
                     'bg-primary',
+                    'o_not_editable',
                 );
                 anchor.href = '#';
                 anchor.contentEditable = "false";