LibDevTools: Add missing return statement in the 'duplicateNode' handler

Author: https://github.com/trflynn89
Commit: 49b964bf19
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3904

Libraries/LibDevTools/Actors/WalkerActor.cpp

@@ -98,6 +98,8 @@ void WalkerActor::handle_message(StringView type, JsonObject const& message)
                     }
                 });
         }
+
+        return;
     }
 
     if (type == "editTagName"sv) {