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

Backport of 0ed7d15563 from master

tests/migrations/test_multidb.py

@@ -1,16 +1,16 @@
 import unittest
 
+from django.db import connection, migrations, models
+from django.db.migrations.state import ProjectState
+from django.test import override_settings
+
+from .test_operations import OperationTestBase
+
 try:
     import sqlparse
 except ImportError:
     sqlparse = None
 
-from django.db import migrations, models, connection
-from django.db.migrations.state import ProjectState
-from django.test import override_settings
-
-from .test_operations import OperationTestBase
-
 
 class AgnosticRouter(object):
     """