Add @since annotation to cancelMany

[isomorpheme]

I wonder if there's a way to lint for this, so it's not forgotten in the future?

[fishtreesugar]

I wonder if there's a way to lint for this, so it's not forgotten in the future?

There's a tool called hackage-diff, but it only works for released versions. I think it might be able to compare with Hackage release candidates.