Fix UnityEventHandlerAsyncEnumerator cancellation

[adarapata]

refs

• OnClickAsAsyncEnumerable(and others) raises event once after cancel called #365

The error in the above issue occurred during the next implementation.

_button.OnClickAsAsyncEnumerable()
    .ForEachAsync(_ => print("push")), token)
    .Forget();

This may be due to the fact that the first TOKEN was used to handle the cancellation of the second TOKEN.

I could see it working in my hand, but I need you to see if it's correct. 🙏

[neuecc]

Oh...!
Thanks, I'll merge and release soon!

[neuecc]

released at 2.3.3.