Add some minor setup behavior to DummyGameTicker by giving it a common base with normal GameTicker.

Necessary for the game to, well, function.

Content.IntegrationTests/DummyGameTicker.cs

@@ -2,14 +2,13 @@ using System;
 using System.Collections.Generic;
 using Content.Server.GameTicking;
 using Content.Server.Interfaces.GameTicking;
-using Content.Shared;
 using Robust.Server.Interfaces.Player;
 using Robust.Shared.Map;
 using Robust.Shared.Timing;
 
 namespace Content.IntegrationTests
 {
-    public class DummyGameTicker : SharedGameTicker, IGameTicker
+    public class DummyGameTicker : GameTickerBase, IGameTicker
     {
         public GameRunLevel RunLevel { get; } = GameRunLevel.InRound;
 
@@ -25,10 +24,6 @@ namespace Content.IntegrationTests
             remove { }
         }
 
-        public void Initialize()
-        {
-        }
-
         public void Update(FrameEventArgs frameEventArgs)
         {
         }