Use PEP 639 license expression

[cdce8p]

Hatchling 1.27.0 added support for PEP 639 license expression. I believe it can be helpful to clarify the licensing situation.
https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license-and-license-files

Ref: #60

Metadata diff

 ...
-License: GPL
+License-Expression: GPL-3.0-or-later OR Apache-2.0
 License-File: COPYING.APACHE
 License-File: COPYING.GPL
 ...
-Classifier: License :: OSI Approved :: Apache Software License
-Classifier: License :: OSI Approved :: GNU General Public License (GPL)
 ...

[tobixen]

Thanks