fix(build): Use SPDX license expression

[cclauss]

Blocked by support for end-of-life Python 3.8

Fix build warnings:

[ ... ] /python3.13/site-packages/setuptools/dist.py:759: SetuptoolsDeprecationWarning:
  License classifiers are deprecated.
!!

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

        License :: OSI Approved :: BSD License

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

!!
  self._finalize_license_expression()

The SPDX license expression was found by reading the top of https://github.com/nodejs/gyp-next/blob/main/LICENSE and then looking up the correct value at https://spdx.org/licenses

[cclauss]

Failing test was fixed in:

• Drop deprecated Python module pkg_resources #333