LibJS: Add missing include to ExecutionContext.h

Userland/Libraries/LibJS/Runtime/ExecutionContext.h

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <AK/FlyString.h>
+#include <AK/WeakPtr.h>
 #include <LibJS/Forward.h>
 #include <LibJS/Runtime/MarkedValueList.h>
 #include <LibJS/Runtime/PrivateEnvironment.h>