[1.8.x] Sorted imports with isort; refs #23860.

Backport of 0ed7d15563 from master

tests/datetimes/tests.py

@@ -3,17 +3,16 @@ from __future__ import unicode_literals
 import datetime
 from unittest import skipIf
 
+from django.test import TestCase, override_settings
+from django.utils import timezone
+
+from .models import Article, Category, Comment
+
 try:
     import pytz
 except ImportError:
     pytz = None
 
-from django.test import TestCase, override_settings
-from django.utils import timezone
-
-
-from .models import Article, Comment, Category
-
 
 class DateTimesTests(TestCase):
     def test_related_model_traverse(self):