Page Cache does not respect 'max-age' = 0

I tried setting headers:dnt and also max-age, but it has no effect. The #attached code is always cached.

Example snippet (change the text to see that the cache is not refreshing):

function mymodule_page_attachments(array &$page) {

  $dnt = (!empty($_SERVER['HTTP_DNT'])) ? [] : ['headers:dnt'];
  $page['#cache']['contexts'] = Cache::mergeContexts(isset($page['#cache']['contexts']) ? $page['#cache']['contexts'] : [], $dnt);
  $page['#cache']['tags'] = Cache::mergeTags(isset($page['#cache']['tags']) ? $page['#cache']['tags'] : [], $config->getCacheTags());
  $page['#cache']['max-age'] = 0;

  $script = 'alert('This is a test.');';
  $page['#attached']['html_head'][] = [
    [
      '#tag' => 'script',
      '#value' => $script,
    ],
    'mymodule_script',
  ];
}

How can I make the script dependend on a lot of rules? Best would be no cache at all.