opengrok-tools: License classifiers are deprecated.

[vladak]

When building the 1.14.0:

* Getting build dependencies for sdist...
/private/var/folders/9r/rmmqdfsn0xv_h9cgnmznpkhr0000gn/T/build-env-m3i2me5x/lib/python3.13/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 :: CDDL

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

!!
  dist._finalize_license_expression()
/private/var/folders/9r/rmmqdfsn0xv_h9cgnmznpkhr0000gn/T/build-env-m3i2me5x/lib/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 :: CDDL

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

!!
  self._finalize_license_expression()

[vladak]

The new format is described on https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license