GHSA-78h3-pg4x-j8cv: libxmljs vulnerable to type confusion when parsing specially crafted XML

libxmljs2 is vulnerable to a type confusion vulnerability when parsing a specially crafted XML while invoking the namespaces() function (which invokes XmlNode::get_local_namespaces()) on a grand-child of a node that refers to an entity. This vulnerability can lead to denial of service and remote code execution.