Fix a problem that notification column goes to top (#4792)

app/javascript/mastodon/features/notifications/index.js

@@ -106,6 +106,7 @@ export default class Notifications extends React.PureComponent {
     const scrollContainer = (
       <ScrollableList
         scrollKey={`notifications-${columnId}`}
+        trackScroll={!pinned}
         isLoading={isLoading}
         hasMore={hasMore}
         emptyMessage={emptyMessage}