minor issues in `writing-pyproject-toml`

Issue Description

In https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license-and-license-files there might be some possible issues:

1. As per PEP 639 licenses should be declared with two fields:

   This reads a bit as if both fields need to be given, but this doesn't seem to follow from PEP 639, unless I've overseen something.

2. The table there says, that setuptools support it since 77.0.3, but setuptools itself seems to claim that it already worked with 77.0.0 ("Support for project.license-files and SPDX license expressions in project.license (PEP 639) were introduced in version 77.0.0."), and AFAICS this is actually the case.

Regards.

Code of Conduct

• I am aware that participants in this repository must follow the PSF Code of Conduct.
  One cannot reasonably assume people to accept a lengthy potentially legally binding document without legal advice for a mere bug report.

Start with the “License and license-files” section of the writing-pyproject-toml guide, then compare its wording with PEP 639 and the linked setuptools documentation and release comparison. Done means clarifying whether both fields are required and correcting the setuptools support version if the evidence confirms it.