Edit Auto Update Admin Notification

by

Try auto_core_update_email. E.g:

add_filter('auto_core_update_email', function($email, $type, $core_update, $result)
{
  if ('success' === $type)
    $email['body'] = sprintf( __('Congratulation! Your site at %1$s has been updated automatically to WordPress %2$s.', 'textdomain'), home_url(), $core_update->current ) . "\n\n";

  return $email;
}, PHP_INT_MAX, 4);