old_contents: __version__ = '0.6.0'
  default_app_config = 'django_undeletable.apps.DjangoUndeletableConfig'
  
new_contents: __version__ = '0.5.1'
  default_app_config = 'django_undeletable.apps.DjangoUndeletableConfig'
  
subject: correct old version to test bumpversion config