Fix MR diff comments. Fix wiki comments loading error

app/contexts/notes/load_context.rb

@@ -20,7 +20,7 @@ module Notes
                  # this is the only case, where the order is DESC
                  project.common_notes.order("created_at DESC, id DESC").limit(50)
                when "wiki"
-                 project.wikis.reverse.map {|w| w.notes.fresh }.flatten[0..20]
+                 project.wiki_notes.limit(20)
                end
 
       @notes = if after_id