src: fix -Winconsistent-missing-override warning

This commit addresses the following warning:

../src/node_api.cc:28:19: warning: 'mark_arraybuffer_as_untransferable'
overrides a member function but is not marked 'override'
      [-Winconsistent-missing-override]
  v8::Maybe<bool> mark_arraybuffer_as_untransferable(
                  ^
../src/js_native_api_v8.h:42:27: note: overridden virtual function is here
  virtual v8::Maybe<bool> mark_arraybuffer_as_untransferable(

PR-URL: #30549
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>

src/node_api.cc

@@ -26,7 +26,7 @@ struct node_napi_env__ : public napi_env__ {
   }
 
   v8::Maybe<bool> mark_arraybuffer_as_untransferable(
-      v8::Local<v8::ArrayBuffer> ab) const {
+      v8::Local<v8::ArrayBuffer> ab) const override {
     return ab->SetPrivate(
         context(),
         node_env()->arraybuffer_untransferable_private_symbol(),