Incompatible with new boot method

[FlorentTorregrosa]

From Core 11.4

https://www.drupal.org/project/drupal/issues/3313404 introduced symfony/runtime and changes in the index.php on how Drupal boot.

Currently it provokes the error:

<b>Fatal error</b>:  Uncaught TypeError: Invalid return value: callable object expected, &quot;int&quot; returned from &quot;/project/www/index.php&quot;. in /project/vendor/autoload_runtime.php:14
Stack trace:
#0 /project/app/autoload_runtime.php(22): require()
#1 /project/app/index.php(13): require_once('/project/app/au...')
#2 /project/www/index.php(4): require('/project/app/in...')
#3 {main}
  thrown in <b>/project/vendor/autoload_runtime.php</b> on line <b>14</b><br />

Because now index.php returns an object:

return static function () {
  return new DrupalKernel('prod', require 'autoload.php');
};