Quit test drivers through ApplicationExit

Drivers finish through ApplicationExit.Quit so engine mods complete their
asynchronous cleanup before the engine shuts down; failure codes are kept.

src/PropertyPatchesTest.cs

@@ -146,7 +146,7 @@ namespace Mods.TestDefaultsAndPatches
         {
             done = true;
             GameLogger.Log("TEST", $"[TEST_RESULT] name={ResultName} passed={passed} failed={failed}");
-            GetTree().Quit(failed == 0 ? 0 : 1);
+            Cthangover.Core.Bootstrap.ApplicationExit.Quit(GetTree(), failed == 0 ? 0 : 1);
         }
     }
 }