LibWeb: Add calls to JS_{DECLARE,DEFINE}_ALLOCATOR()

Author: https://github.com/mattco98
Commit: 31341b280a
Pull-request: https://github.com/SerenityOS/serenity/pull/23878
Issue: https://github.com/SerenityOS/serenity/issues/23805
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibWeb/CSS/AnimationEvent.h

@@ -21,6 +21,7 @@ struct AnimationEventInit : public DOM::EventInit {
 // https://www.w3.org/TR/css-animations-1/#animationevent
 class AnimationEvent : public DOM::Event {
     WEB_PLATFORM_OBJECT(AnimationEvent, DOM::Event);
+    JS_DECLARE_ALLOCATOR(AnimationEvent);
 
 public:
     [[nodiscard]] static JS::NonnullGCPtr<AnimationEvent> create(JS::Realm&, FlyString const& type, AnimationEventInit const& event_init = {});