Support Django 5.0 db_default attribute.

A DB default is not considered backward incompatible, as the default value is kept on DB-level.
See https://docs.djangoproject.com/en/dev/releases/5.0/#database-computed-default-values

tests/fixtures.py

@@ -8,6 +8,9 @@ RENAME_COLUMN = "app_rename_column"
 RENAME_TABLE = "app_rename_table"
 IGNORE_MIGRATION = "app_ignore_migration"
 ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DEFAULT = "app_add_not_null_column_followed_by_default"
+ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DB_DEFAULT = (
+    "app_add_not_null_column_followed_by_db_default"
+)
 ALTER_COLUMN = "app_alter_column"
 ALTER_COLUMN_DROP_NOT_NULL = "app_alter_column_drop_not_null"
 DROP_UNIQUE_TOGETHER = "app_unique_together"