[1.6.x] Fixed a test that was failing with PostGIS.

Fixed #21452 again.

tests/backends/tests.py

@@ -363,11 +363,12 @@ class PostgresNewConnectionTests(TestCase):
         after setting the time zone when AUTOCOMMIT is False (#21452).
         """
         databases = copy.deepcopy(settings.DATABASES)
+        databases[DEFAULT_DB_ALIAS]['AUTOCOMMIT'] = False
         new_connections = ConnectionHandler(databases)
         new_connection = new_connections[DEFAULT_DB_ALIAS]
         try:
-            new_connection.settings_dict['AUTOCOMMIT'] = False
-            cursor = new_connection.cursor()
+            # Open a database connection.
+            new_connection.cursor()
             self.assertFalse(new_connection.get_autocommit())
         finally:
             new_connection.close()