Tests/LibWeb: Prove we do not fail serialization of empty strings

Author: https://github.com/kennethmyhra
Commit: 77b1469900
Pull-request: https://github.com/SerenityOS/serenity/pull/23438
Reviewed-by: https://github.com/ADKaster ✅

Tests/LibWeb/Text/input/HTML/StructuredClone-primitives.html

@@ -8,6 +8,7 @@
         println(structuredClone(123));
         println(structuredClone(123.456));
         println(structuredClone(BigInt("0x1fffffffffffff")))
+        println(structuredClone(""));
         println(structuredClone("This is a string"));
     });
 </script>