LibWeb: Port EventTarget to new {Fly}String

Author: https://github.com/kennethmyhra
Commit: 2091a11488
Pull-request: https://github.com/SerenityOS/serenity/pull/18255
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.cpp

@@ -30,9 +30,9 @@ void HTMLFrameSetElement::parse_attribute(DeprecatedFlyString const& name, Depre
     HTMLElement::parse_attribute(name, value);
 
 #undef __ENUMERATE
-#define __ENUMERATE(attribute_name, event_name)                     \
-    if (name == HTML::AttributeNames::attribute_name) {             \
-        element_event_handler_attribute_changed(event_name, value); \
+#define __ENUMERATE(attribute_name, event_name)                                                                     \
+    if (name == HTML::AttributeNames::attribute_name) {                                                             \
+        element_event_handler_attribute_changed(event_name, String::from_deprecated_string(value).release_value()); \
     }
     ENUMERATE_WINDOW_EVENT_HANDLERS(__ENUMERATE)
 #undef __ENUMERATE