Use CancellationToken.None for cleanup in .NET cancellation example

docs/develop/dotnet/workflows/cancellation.mdx

@@ -90,15 +90,18 @@ public async Task RunAsync()
 
         // Call cleanup activity. If this throws, it will swallow the original exception which we
         // are ok with here. This could be changed to just log a failure and let the original
-        // cancellation continue. We use a different cancellation token since the default one on
-        // Workflow.CancellationToken is now marked cancelled.
-        using var detachedCancelSource = new CancellationTokenSource();
+        // cancellation continue. 
+        // The default token on Workflow.CancellationToken is now marked
+        // cancelled, so we pass a different one. We use CancellationToken.None here because the
+        // cleanup activity itself doesn't need to be cancellable; if it did (e.g. you want to
+        // cancel cleanup from a timeout or another signal), create a new detached
+        // CancellationTokenSource and pass its Token instead.
         await Workflow.ExecuteActivityAsync(
             (MyActivities a) => a.MyCancellationCleanupActivity(),
             new()
             {
                 ScheduleToCloseTimeout = TimeSpan.FromMinutes(5),
-                CancellationToken = detachedCancelSource.Token;
+                CancellationToken = CancellationToken.None,
             });
 
         // Rethrow the cancellation