Fix deprecation notice in PHP 8 for libxml_disable_entity_loader
Fix deprecation notice in PHP 8 for libxml_disable_entity_loader

PHP 8 [deprecates `libxml_disable_entity_loader`](https://php.watch/versions/8.0/libxml_disable_entity_loader-deprecation) function, and this fixes the deprecation notice by not calling the function on libxml 2.9, where external entity loader is disabled by default and is not necessary to explicitly disable it.

Imangazaliev/DiDOM