Fix license in pyproject.toml to be compatible with PEP 621

[Bluefissure]

Update pyproject.toml to change the license field compatible with PEP 621

I'm not sure which is the best way to resolve this as the license is deprecated in a following PEP 639 (which introduces License-Expression), but making this change will at least making new pip version (> 23.0.1) not complaining.

[mattip]

LGTM, pending CI completion. This is the same form of the pyproject.toml in scipy.

[EpicWink]

See my comment:

license being a (inline) table is deprecated, and should be a string (identifying the license). See:

• pyproject.toml guide
• license in pyproject.toml spec
• License expression spec

Try using Setuptools v77.0.3 or later. If your version of Python can't support that, try constraining cffi to below v2

The real fix here is to have cffi require setuptools >= 77.0.3 in its pyproject.toml

[adamjstewart]

I don't understand. We had a pyproject.toml that satisfied PEP 639. Then this PR undid this to return to a deprecated specification?

[Bluefissure]

I don't understand. We had a pyproject.toml that satisfied PEP 639. Then this PR undid this to return to a deprecated specification?

Yes, I think the required setuptools >= 66.1 does not support PEP 639, we need to update that if we want to change it to PEP 639.

Oh just saw your PR, thanks!