GHSA-mg49-jqgw-gcj6: libxmljs vulnerable to type confusion when parsing specially crafted XML

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