Noticed this when building 4.0.0.dev0

SetuptoolsDeprecationWarning: project.license as a TOML table is deprecated
Please use a simple string containing a SPDX expression for project.license. You can also use project.license-files. (Both options available on setuptools>=77.0.0).
By 2026-Feb-18, you need to update your project and remove deprecated calls or your builds will no longer be supported.
See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.