Fix compatibility with Python 3.12, Stop using python setup.py test, Use PEP 517 workflow, Use SPDX license

• Fix compatibility with Python 3.12.
  • Cherry-pick fix Python 3.12's removal of the imp module 1. Requires first cherry-picking 2 which removes dependency on python-six.
  • Fixes #1 (closed).
• Change to a PEP 517 based workflow and call unittest module directly
• Change to SPDX license identifier
  • https://github.com/sphinx-contrib/autoprogram/blob/b6df97b08e1c28684911f7704422da074d4c4e27/setup.py#L24
  • https://github.com/sphinx-contrib/autoprogram/blob/b6df97b08e1c28684911f7704422da074d4c4e27/LICENSE