gh-152313: bump pixi-packages to 3.16

[lucascolley]

• Issue: bump pixi-packages to 3.16 #152313

see https://github.com/python/cpython/blob/main/Tools/pixi-packages/README.md#maintenance

[lucascolley]

hey @savannahostrowski, maybe this falls under your RM remit :)

[StanFromIreland]

There were talks previously about making this more future proof?

If that's not possible we should add this to the RMs todo list in release-tools.

[lucascolley]

There were talks previously about making this more future proof?

There is a comment in the README about combining these into a single pixi.toml file. That might be possible now that the latest Pixi release shipped https://pixi.prefix.dev/latest/concepts/package_specifications/#extras-and-flags — I'll look into it in a separate PR.

There was also a discussion about having a source-of-truth file somewhere storing 3.16 that other files could reference dynamically. I'd be open to that, or to automating updates. Also happy to add it to the RM list in the meantime if that sounds alright.

[StanFromIreland]

I'm not familiar with Pixi (I'm also not sure why we need to have these scripts, other distributors have them in their own repos.), so I'm afraid I won't be of any help here. As for adding it to the RM's workload, see this PR: python/release-tools#382.