Suppress warnings generated by DOMDocument::loadHTML()

[ocean90]

DOMDocument::loadHTML() may throw some PHP warnings for unknown HTML. To suppress them we can use libxml_use_internal_errors(false).

Some logged warnings:

WordPress is doing the same in several places:

• https://github.com/WordPress/wordpress-develop/blob/2648a5f984b8abf06872151898e3a61d3458a628/src/wp-includes/widgets/class-wp-widget-text.php#L128
• https://github.com/WordPress/wordpress-develop/blob/2648a5f984b8abf06872151898e3a61d3458a628/src/wp-includes/class-wp-oembed.php#L612
• https://github.com/WordPress/wordpress-importer/blob/e05f678835c60030ca23c9a186f50999e198a360/src/parsers/class-wxr-parser-simplexml.php#L20