Refs #30057 -- Added more diffsettings tests.

The test in 573f44d62f doesn't act as a
regression test.

tests/admin_scripts/configured_dynamic_settings_manage.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python
+import sys
+
+from django.conf import global_settings, settings
+from django.core.management import execute_from_command_line
+
+
+class Settings:
+    def __getattr__(self, name):
+        if name == 'FOO':
+            return 'bar'
+        return getattr(global_settings, name)
+
+    def __dir__(self):
+        return super().__dir__() + dir(global_settings) + ['FOO']
+
+
+if __name__ == '__main__':
+    settings.configure(Settings())
+    execute_from_command_line(sys.argv)