Seal/abstract/virtual everything (#6739)

Content.Server/Ghost/GhostSystem.cs

@@ -23,7 +23,7 @@ using Robust.Shared.Timing;
 namespace Content.Server.Ghost
 {
     [UsedImplicitly]
-    public class GhostSystem : SharedGhostSystem
+    public sealed class GhostSystem : SharedGhostSystem
     {
         [Dependency] private readonly IGameTiming _gameTiming = default!;
         [Dependency] private readonly IPlayerManager _playerManager = default!;