Update pyproject license schema according to deprecation warnings

[maresb]

* Building wheel... /tmp/build-env-vi5sasbz/lib/python3.12/site-packages/setuptools/config/_apply_pyprojecttoml.py:82: 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.
        ********************************************************************************
!!
  corresp(dist, value, root_dir)
/tmp/build-env-vi5sasbz/lib/python3.12/site-packages/setuptools/config/_apply_pyprojecttoml.py:61: 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.
        ********************************************************************************

Description

Related Issue

• Closes #
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

---

📚 Documentation preview 📚: https://pytensor--1362.org.readthedocs.build/en/1362/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.05%. Comparing base (0c398e3) to head (74378de).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1362   +/-   ##
=======================================
  Coverage   82.05%   82.05%           
=======================================
  Files         203      203           
  Lines       48863    48863           
  Branches     8695     8695           
=======================================
  Hits        40093    40093           
  Misses       6619     6619           
  Partials     2151     2151           

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