LibWeb: Fix a few const-ness issues

Author: https://github.com/mattco98
Commit: c0b2fa74ac
Pull-request: https://github.com/SerenityOS/serenity/pull/17620
Issue: https://github.com/SerenityOS/serenity/issues/16988
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp

@@ -256,7 +256,7 @@ void queue_global_task(HTML::Task::Source source, JS::Object& global_object, JS:
 }
 
 // https://html.spec.whatwg.org/#queue-a-microtask
-void queue_a_microtask(DOM::Document* document, JS::SafeFunction<void()> steps)
+void queue_a_microtask(DOM::Document const* document, JS::SafeFunction<void()> steps)
 {
     // 1. If event loop was not given, set event loop to the implied event loop.
     auto& event_loop = HTML::main_thread_event_loop();