[5.0.x] Applied Black's 2024 stable style.

https://github.com/psf/black/releases/tag/24.1.0

Backport of 305757aec1 from main

tests/backends/tests.py

@@ -1,4 +1,5 @@
 """Tests related to django.db.backends that haven't been organized."""
+
 import datetime
 import threading
 import unittest