Fix PageQuerySet code overriding code snippet

docs/topics/pages.rst

@@ -474,4 +474,4 @@ Alternately, if you only need to add extra ``QuerySet`` methods, you can inherit
     class EventPage(Page):
         start_date = models.DateField()
 
-        objects = PageManager.from_queryset(EventQuerySet)
+        objects = PageManager.from_queryset(EventPageQuerySet)