Add support for Python v3.12

Expected to be release the 2nd October 2023.

• Introduce Python 3.12 image generation (docker/python3/poetry#8 - closed): Unstable image in the meantime: using rc with gcc and libffi-dev installed
• Set up v3.12 test job
  • Set allow_failure = True
• Introduce Python 3.12 image generation (docker/python3/poetry#8 - closed): Use stable tag (without rc) Remove gcc and libffi-dev installations
• Move coverage to v3.12 job
• Set default container to v3.12 (would require pre-commit and git to be installed)
• Handle deprecation warning and breaking features
• Open follow-up v3.13 tickets: Add support for Python v3.13 (#208 - closed)