LibWeb: Don't crash when cloning a CDATASection node

Author: https://github.com/tcl3
Commit: 72ed62a560
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/798
Reviewed-by: https://github.com/AtkinsSJ ✅
Reviewed-by: https://github.com/trflynn89

Tests/LibWeb/Text/input/DOM/CDATASection-cloneNode.html

@@ -0,0 +1,9 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        const xmlDocument = new DOMParser().parseFromString(`<xml></xml>`, "application/xml");
+        const cdata = xmlDocument.createCDATASection("PASS");
+        const clone = cdata.cloneNode();
+        println(`Cloned CDATASection node data: ${clone.data}`);
+    });
+</script>