Add support for Python v3.12

Expected to be release the 2nd October 2023.

• Introduce Python 3.12 image generation (docker/python3/poetry#8)
• Add support for Python v3.12 (duniterpy#196)
• Set up v3.12 test job
  • Remove allow_failure: true, now on the tests should pass
• Move coverage to v3.12 job
• Switch Silkaj container to v3.12
• Set default container to v3.12
• Handle deprecation warning and breaking features
  • No wheel provided for pendulum v2.1.2 for Py3.12. Setting 3.0.0a1 solves the issue, because there is wheels (built C code) provided till Py3.11 (it’s most likely taking previous Python version, until Python 3.12 is released as stable)
  • Switch pendulum to a stable version once there is a wheel provided for Py3.12
• Switch image to v3.12
• Open follow-up v3.13 tickets