Fix upstream CS9104 compile error

This should let us build the project again while we wait for the upstream fix.

Barotrauma/BarotraumaClient/ClientSource/Networking/ServerList/PingUtils.cs

@@ -53,7 +53,7 @@ namespace Barotrauma.Networking
             }
         }
 
-        private readonly ref struct LobbyDataChangedEventHandler
+        private readonly struct LobbyDataChangedEventHandler : IDisposable
         {
             private readonly Action<Lobby> action;