LibWasm: Store function references' source module in RefPtr to const

Author: https://github.com/ADKaster
Commit: 16e764ddb6
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4362
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/Hendiadyoin1

Libraries/LibWasm/AbstractMachine/AbstractMachine.h

@@ -51,7 +51,7 @@ public:
     };
     struct Func {
         FunctionAddress address;
-        RefPtr<Module> source_module; // null if host function.
+        RefPtr<Module const> source_module; // null if host function.
     };
     struct Extern {
         ExternAddress address;