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.h

@@ -115,7 +115,7 @@ private:
 EventLoop& main_thread_event_loop();
 void old_queue_global_task_with_document(HTML::Task::Source, DOM::Document&, JS::SafeFunction<void()> steps);
 void queue_global_task(HTML::Task::Source, JS::Object&, JS::SafeFunction<void()> steps);
-void queue_a_microtask(DOM::Document*, JS::SafeFunction<void()> steps);
+void queue_a_microtask(DOM::Document const*, JS::SafeFunction<void()> steps);
 void perform_a_microtask_checkpoint();
 
 }