PDF export can hang indefinitely if the headless Chrome crashes or is stopped

Follow these steps to reproduce:

• Create a wiki page with some simple test content
• Add a JSX object to this page, with this content:

  require(['xwiki-page-ready'], function(pageReady) {
    pageReady.delayPageReady(new Promise((resolve, reject) => {
      // Delay the page ready with 55 seconds.
      setTimeout(resolve, 55 * 1000);
    }), 'simulate long PDF export');
  });
  

• Configure the JSX with:
  • Use on this page or on demand
  • No parsing
• Make sure PDF export is configured to use the headless Chrome Docker container; keep the default 60 seconds page ready timeout
• Export the page to PDF
• While the PDF export is running (in fact it is waiting for the page to be ready before printing to PDF) stop the headless Chrome Docker container

Expected: the PDF export should fail, at most after the 60 seconds page ready timeout.
Actual: the PDF export keeps running beyond those 60 seconds. In fact, it will keep waiting for the page to be ready until you restart XWiki or use some script to kill the background thread used by the PDF export job.