Fix: fix setuptools deprecation warning

[pjonsson]

Description

Use the SPDX expression for license
classifier and remove the now deprecated
TOML table license according to this warning
in the CI jobs:

        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 2027-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.

and:

dist.py:765: SetuptoolsDeprecationWarning: License classifiers are deprecated.
!!

        ********************************************************************************
        Please consider removing the following classifiers in favor of a SPDX license expression:

        License :: OSI Approved :: MIT License

        See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
        ********************************************************************************

!!

Checklist

This pull request is:

• A documentation / typographical error fix
  • Good to go, no issue or tests are needed
• A short code fix
  • Please include: Fixes: #<issue number> in the description if it solves an existing issue
    (which must include a complete example of the issue).
  • Please include tests that fail with the main branch and pass with the provided fix.
• A new feature implementation or update an existing feature
  • Please include: Fixes: #<issue number> in the description if it solves an existing issue
    (which must include a complete example of the feature).
  • Please include tests that cover every lines of the new/updated feature.
  • Please update the documentation to describe the new/updated feature.

[adrien-berchet]

Hi @pjonsson
Thanks for this, I missed this warning!