[28222] Label video modal with close

It's currently not used on first login as far as I can tell

https://community.openproject.com/wp/28222

[ci skip]

app/views/onboarding/_onboarding_video_modal.html.erb

@@ -53,7 +53,7 @@ See docs/COPYRIGHT.rdoc for more details.
     <div class="onboarding--footer op-modal--modal-footer">
       <em><label><%= I18n.t('onboarding.text_show_again') %></label></em>
       <button class="dynamic-content-modal--close-button button -highlight -large"
-              title=<%= t(:label_next)%>> <%= t(:label_next)%>
+              title=<%= t(:button_close)%>> <%= t(:button_close)%>
       </button>
     </div>
   </div>