Description:
------------
This patch deprecated the libxml_disable_entity_loader function: https://github.com/php/php-src/pull/5867. However, XXE attacks are still possible if not calling it.


Running this command will demonstrate the problem:
docker run -ti --rm -v $(pwd):/tmp/test php:8.0-rc-cli-alpine php /tmp/test/test.php

Where test.php is the script provided here.

Test script:
---------------
<?php

//libxml_disable_entity_loader();
$doc = new DOMDocument();

$doc->schemaValidateSource(<<<XSD
<?xml version="1.0" encoding="utf-8" ?>
<xsd:schema xmlns="http://symfony.com/schema"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    targetNamespace="http://symfony.com/schema"
    elementFormDefault="qualified">

    <xsd:import namespace="http://www.w3.org/XML/1998/namespace"/>
  <xsd:import namespace="http://symfony.com/schema/dic/services" schemaLocation="https://webhook.site/203bf182-524d-4133-ad37-7865ecde5749" />

</xsd:schema>
XSD
);


Expected result:
----------------
You should see this warning:
Warning: DOMDocument::schemaValidateSource(): Element '{http://www.w3.org/2001/XMLSchema}import': Failed to locate a schema at location 'https://webhook.site/203bf182-524d-4133-ad37-7865ecde5749'. Skipping the import. in /tmp/test/test.php on line 7

And PHP should NOT try to load the resource

Actual result:
--------------
You see this warning:
Warning: DOMDocument::schemaValidateSource(): Element '{http://www.w3.org/2001/XMLSchema}import': Failed to parse the XML resource 'https://webhook.site/203bf182-524d-4133-ad37-7865ecde5749'. in /tmp/test/test.php on line 7


And PHP tries to make a HTTP request