[FIX] website_slides: correctly hide "quiz finish" modal on "Next" button

This commit fixes the "quiz finish" modal display by correctly hiding it when the user clicks on
the "Next" button in the modal.

Without this fix, the user could run into an issue where the "modal backdrop" would stay on the
screen, locking all actions and forcing a manual refresh.

Task#2118532

closes odoo/odoo#39899

X-original-commit: 84603c6d928e5ba9b19c4ed3e8b6edbab42a8a5b
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/website_slides/static/src/js/slides_course_quiz.js

@@ -339,6 +339,9 @@ odoo.define('website_slides.quiz', function (require) {
          */
         _onClickNext: function (ev) {
             if (this.slide.hasNext) {
+                if (this.$('#slides_quiz_modal').length !== 0) {
+                    this.$('#slides_quiz_modal').modal('hide');
+                }
                 this.trigger_up('slide_go_next');
             }
         },