Fix token param in force_authenticate example (#5284)

related_name for Token is `auth_token`, not `token`.

docs/api-guide/testing.md

@@ -82,7 +82,7 @@ For example, when forcibly authenticating using a token, you might do something
 
     user = User.objects.get(username='olivia')
     request = factory.get('/accounts/django-superstars/')
-    force_authenticate(request, user=user, token=user.token)
+    force_authenticate(request, user=user, token=user.auth_token)
 
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