`withError` lacks a `@since` annotation

[andreasabel]

withError lacks a @since annotation: https://hackage.haskell.org/package/mtl-2.3.1/docs/Control-Monad-Error-Class.html#v:withError I think this hasn't been in mtl forever, e.g. missing still in mtl-2.2.2: https://hackage.haskell.org/package/mtl-2.2.2/docs/Control-Monad-Error-Class.html#v:withError Hit me in the wild at: https://github.com/agda/agda/actions/runs/11103657461/job/30846087778?pr=7519#step:11:423

Probably some more functions that entered in mtl-2.3 need such an annotation.

[andreasabel]

ATTN: @emilypi

[emilypi]

I can add an annotation here. Any gripes @kozross?

[kozross]

None from me.

[meipp]

This was done in 7e51363 but hasn't been released yet