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

Backport of 0ed7d15563 from master

tests/foreign_object/models.py

@@ -1,7 +1,8 @@
 import datetime
 
 from django.db import models
-from django.db.models.fields.related import ReverseSingleRelatedObjectDescriptor
+from django.db.models.fields.related import \
+    ReverseSingleRelatedObjectDescriptor
 from django.utils.encoding import python_2_unicode_compatible
 from django.utils.translation import get_language