Use PEP 517 workflow, Replace python-pytest-runner, Use SPDX license

• Change to a PEP 517 based workflow
• Replace python-pytest-runner with python-pytest
• Change to SPDX license identifier
  • https://github.com/kmike/text-unidecode/blob/1.3/LICENSE

For the SPDX change PerlArtistic becomes Artistic-1.0-Perl. LICENSE contains:

text-unidecode is a free software; you can redistribute
it and/or modify it under the terms of either:

* GPL or GPLv2+ (see https://www.gnu.org/licenses/license-list.html#GNUGPL), or
* Artistic License - see below:

setup.py contains:

        'License :: OSI Approved :: Artistic License',
        'License :: OSI Approved :: GNU General Public License (GPL)',
        'License :: OSI Approved :: GNU General Public License v2 or later (GPLv2+)',