core&ui: fix contest_edit file upload

packages/ui-default/templates/contest_edit.html

@@ -233,7 +233,7 @@
       <div class="section__header">
         <h1 class="section__title">{{ _('Files') }}</h1>
         <div class="section__tools">
-          <button class="primary rounded button" name="upload_file">{{ _('Upload') }}</button>
+          <button class="primary rounded button" name="upload_file" data-type="public" data-sidebar="true">{{ _('Upload') }}</button>
         </div>
       </div>
       {% set sidebar = true %}