docs: def site_models(self, app_label=None):
          """Returns a dictionary of registered models.
          """
          site_models = {}
          app_configs = (
              django_apps.get_app_configs()
              if app_label is None
              else [django_apps.get_app_config(app_label)]
          )
          for app_config in app_configs:
              model_list = [
                  model
                  for model in app_config.get_models()
                  if model._meta.label_lower in self.registry
              ]
              if model_list:
                  model_list.sort(key=lambda m: m._meta.verbose_name)
                  site_models.update({app_config.name: model_list})
          return site_models