CI: Use Python 3.12 for exercising native Python test layers

[amotl]

About

The "native" tests do not succeed on Python 3.12 yet, cr8 needs a corresponding fix.

  File "/path/to/cratedb-examples/testing/native/python-unittest/test_unittest.py", line 12, in <module>
    from cr8.run_crate import create_node
  File "/path/to/cratedb-examples/.venv312/lib/python3.12/site-packages/cr8/__init__.py", line 1, in <module>
    import pkg_resources
ModuleNotFoundError: No module named 'pkg_resources'

[amotl]

There is a corresponding patch now, which will resolve this.

• Maintenance: Add support for Python 3.12  mfussenegger/cr8#371