Make tests automatically reset modified cvars (#28219)

* Make tests automatically reset modified cvars

* Fix bad return

* A

* Try Fix tests

* clarify comment

* update eng

Content.IntegrationTests/PoolManager.cs

@@ -270,6 +270,8 @@ public static partial class PoolManager
             $"{nameof(GetServerClientPair)}: Retrieving pair {pair.Id} from pool took {poolRetrieveTime.TotalMilliseconds} ms");
         await testOut.WriteLineAsync(
             $"{nameof(GetServerClientPair)}: Returning pair {pair.Id}");
+
+        pair.ClearModifiedCvars();
         pair.Settings = poolSettings;
         pair.TestHistory.Add(currentTestName);
         pair.Watch.Restart();