[FIX] website_slides: prevent flicker on hover

This commit fixes the flicker issue of buttons hovering over content
on the course page.

Task-3751285

closes odoo#155869

Signed-off-by: Warnon Aurélien (awa) <awa@odoo.com>

addons/website_slides/views/website_slides_templates_course.xml

@@ -498,7 +498,7 @@
             </span>
         </div>
 
-        <div class="d-flex flex-row">
+        <div class="d-flex flex-row align-items-center">
             <a name="o_wslides_list_slide_add_quizz" t-if="channel.can_upload and not slide.question_ids" t-attf-href="/slides/slide/#{slug(slide)}?quiz_quick_create">
                 <span class="badge badge-light badge-hide border font-weight-normal px-2 py-1 m-1">Add Quiz</span>
             </a>