old_contents: from django.apps import AppConfig
  
  from health_check.plugins import plugin_dir
  
  
  class HealthCheckConfig(AppConfig):
      name = 'health_check.db'
  
      def ready(self):
          from .backends import DatabaseBackend
          plugin_dir.register(DatabaseBackend)
  
new_contents: from django.apps import AppConfig
  
  from health_check.plugins import plugin_dir
  
  
  class HealthCheckConfig(AppConfig):
      default_auto_field = 'django.db.models.AutoField'
      name = 'health_check.db'
  
      def ready(self):
          from .backends import DatabaseBackend
          plugin_dir.register(DatabaseBackend)
  
subject: Add default_auto_field to satisfy Django 4.0 (#292)