Standardized calling decorators on contrib.auth views.

[claudep]

With the addition of login_not_required decorator on contrib.auth views for Django 5.1, the various views are decorated sometimes on the class itself, sometimes on the dispatch method, sometimes on both. IMHO, it would be cleaner to use only one way and group all decorators for a same class, like https://docs.djangoproject.com/en/5.1/topics/class-based-views/intro/#decorating-the-class suggests.