revert: "temp: reverse stack order of discussions and upsell in sidebar (#1705)" (#1712)

This reverts commit 2ce833341b.

src/courseware/course/new-sidebar/sidebars/discussions-notifications/DiscussionsNotificationsSidebar.tsx

@@ -21,9 +21,9 @@ const DiscussionsNotificationsSidebar = () => {
       showTitleBar={false}
       showBorder={false}
     >
-      <DiscussionsSidebar />
-      {!hideNotificationbar && <div className="my-1.5" />}
       <NotificationTray />
+      {!hideNotificationbar && <div className="my-1.5" />}
+      <DiscussionsSidebar />
     </SidebarBase>
   );
 };