Bump packaging >= 26.1

[woodruffw]

This is tripping the CI in #1309 and on main.

packaging==26.1 moves packaging.metadata.ExceptionGroup to packaging.errors.ExceptionGroup, but re-exports that API through packaging.metadata for backwards compatibility. However, that re-export isn't explicitly marked in __all__, so mypy flags it.

We could patch around this or suppress it, but bumping to >= 26.1 is easiest.

Here's the implicit re-export:

https://github.com/pypa/packaging/blob/b82413d6a1e5037b65aabc44154a97f0b2d63766/src/packaging/metadata.py#L21

CC @henryiii for opinions since I think packaging.errors was your change with pypa/packaging#1071 🙂

[sigmavirus24]

What if we bump the minimum packaging version to not encounter this and clean things up instead of adding the mypy ignore?

[woodruffw]

What if we bump the minimum packaging version to not encounter this and clean things up instead of adding the mypy ignore?

That works for me! That'll be a big bump in terms of downstream integrators (since right now we test packaging==24 as a supported variant, but I think it's good to nudge integrators to stay closer to the newer edge of PyPA tooling 🙂

[henryiii]

We can add it to __all__ for 26.2. Might be nice to for a release or two to give users a chance to move before seeing mypy warnings, or to help keep it easy to maintain older versions too.