[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/proxy_models/models.py

@@ -4,6 +4,7 @@ they will take data directly from the table of their base class table rather
 than using a new table of their own. This allows them to act as simple proxies,
 providing a modified interface to the data from the base class.
 """
+
 from django.db import models
 
 # A couple of managers for testing managing overriding in proxy model cases.