[3.1.x] Bumped minimum isort version to 5.1.0.

Fixed inner imports per isort 5.
isort 5.0.0 to 5.1.0 was unstable.

Backport of e74b3d724e from master

tests/backends/postgresql/test_creation.py

@@ -13,6 +13,7 @@ except ImportError:
     pass
 else:
     from psycopg2 import errorcodes
+
     from django.db.backends.postgresql.creation import DatabaseCreation
 
 

tests/backends/postgresql/tests.py

@@ -129,10 +129,10 @@ class Tests(TestCase):
             ISOLATION_LEVEL_READ_COMMITTED as read_committed,
             ISOLATION_LEVEL_SERIALIZABLE as serializable,
         )
+
         # Since this is a django.test.TestCase, a transaction is in progress
         # and the isolation level isn't reported as 0. This test assumes that
         # PostgreSQL is configured with the default isolation level.
-
         # Check the level on the psycopg2 connection, not the Django wrapper.
         default_level = read_committed if psycopg2.__version__ < '2.7' else None
         self.assertEqual(connection.connection.isolation_level, default_level)