Merge branch 'ph/extensionBorders' into 'master'

Fix widget extension container not having bottom border

See merge request gitlab-org/gitlab!89755

app/assets/javascripts/vue_merge_request_widget/components/extensions/container.js

@@ -14,7 +14,7 @@ export default {
     if (extensions.length === 0) return null;
 
     return h(
-      'div',
+      'section',
       {
         attrs: {
           role: 'region',