Fix course about page video. (#22775)

PROD-1124

lms/templates/video_modal.html

 <%page expression_filter="h"/>
 <%!
   from lms.djangoapps.courseware.courses import get_course_about_section
+  from openedx.core.djangolib.markup import HTML
 %>
 <%namespace name='static' file='static_content.html'/>
 
 <div id="video-modal" class="modal video-modal">
   <div class="inner-wrapper">
-    ${get_course_about_section(request, course, "video")}
+    ${HTML(get_course_about_section(request, course, "video"))}
   </div>
 </div>