[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/postgres_tests/fields.py

@@ -2,6 +2,7 @@
 Indirection layer for PostgreSQL-specific fields, so the tests don't fail when
 run with a backend other than PostgreSQL.
 """
+
 import enum
 
 from django.db import models