[5.1.x] Fixed typo in tutorial 5.

Backport of 095f5db from main.

Author: cliff688

docs/intro/tutorial05.txt

@@ -456,7 +456,7 @@ and then we must amend the ``get_queryset`` method like so:
 
 ``Question.objects.filter(pub_date__lte=timezone.now())`` returns a queryset
 containing ``Question``\s whose ``pub_date`` is less than or equal to - that
-is, earlier than or equal to - ``timezone.now``.
+is, earlier than or equal to - ``timezone.now()``.
 
 Testing our new view
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