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/HTML/Scripting/Fetching.cpp

@@ -28,6 +28,8 @@
 
 namespace Web::HTML {
 
+JS_DEFINE_ALLOCATOR(FetchContext);
+
 OnFetchScriptComplete create_on_fetch_script_complete(JS::Heap& heap, Function<void(JS::GCPtr<Script>)> function)
 {
     return JS::create_heap_function(heap, move(function));