http2: fix compilation error after V8 update

Backport-PR-URL: #14813
Backport-Reviewed-By: Anna Henningsen <anna@addaleax.net>
Backport-Reviewed-By: Timothy Gu <timothygu99@gmail.com>

PR-URL: #14239
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

src/node_http2.cc

@@ -868,7 +868,7 @@ void Http2Session::OnTrailers(Nghttp2Stream* stream,
     };
 
     Local<Value> ret = MakeCallback(env()->ontrailers_string(),
-                                    arraysize(argv), argv);
+                                    arraysize(argv), argv).ToLocalChecked();
     if (!ret.IsEmpty()) {
       if (ret->IsArray()) {
         Local<Array> headers = ret.As<Array>();