Pin `packaging` version

[SnoopJ]

@Exirel discovered that we have some problems with type analysis on master if one has a packaging version that is 'too old'.

$ mypy --check-untyped-defs sopel
sopel/lifecycle.py:147: error: Unsupported operand types for >= ("tuple[int, ...]" and "None")  [operator]
sopel/lifecycle.py:147: note: Right operand is of type "tuple[int, ...] | None"

The above was observed with packaging==21.3.

I tried to look in their changelog to see if there was a specific version that fixed the issue we saw, but came up empty-handed. Pinning the lower bound to the latest version is the next best thing to do, and this package has excellent compatibility, so it shouldn't be a problem.

Checklist

• [x] I have read CONTRIBUTING.md
• [x] I can and do license this contribution under the EFLv2
• [x] No issues are reported by make qa (runs make lint and make test)
• [x] I have tested the functionality of the things this change touches

[dgw]

After some question about dropping back to earliest-good after I found the source of mypy considering the version's release property optional (tuple[...] | None), we elected to just keep this latest-good release constraint. It's fine.