WaitHandle.Dispose – diposing is not necessary

From [WaitHandle.Dispose Method](https://docs.microsoft.com/en-us/dotnet/api/system.threading.waithandle.dispose?view=net-6.0#System_Threading_WaitHandle_Dispose)

> Note
>
> Always call Close or Dispose() before you release your last reference to the WaitHandle. Otherwise, the resources it is using will not be freed.

While fact that `WaitHandle` uses `SafeWaitHandle` that will be finalized when `Dispose` not called is implementation detail, I guess this note better avoid direct lying. I cannot tell for previous version though.