chore: upgrade GitHub workflows

[leszekhanusz]

• Bump GitHub actions:

  • actions/checkout@v4
  • actions/setup-python@v5
  • codecov/codecov-action@v4

• Bump Ubuntu 20.04 to 24.04

• Bump default Python version to 3.12 instead of 3.8

• Bump pypy version to 3.10 instead of 3.8

With Python 3.12, the following dev/tests dependencies needed to be updated:

• pytest-console-scripts to 1.4.1
• flake8 to 7.1.1