ci: Run tests on Python 3.11

[slovdahl]

No description provided.

[slovdahl]

This does not seem to work yet.. The current Poetry version does not seem to work with Python 3.11, and the next version requires Python 3.7+.

[slovdahl]

Hmm.. Linting fails with some strange errors too. Sounds like pylint-dev/pylint#6535.

=================================== FAILURES ===================================
__________________________ [pylint] tests/test_app.py __________________________
E: 46,15: Module 'os' has no 'environ' member (no-member)
E: 48, 4: Module 'os' has no 'environ' member (no-member)
E: 50, 8: Module 'os' has no 'environ' member (no-member)
E: 54, 4: Module 'os' has no 'environ' member (no-member)
E: 56, 8: Module 'os' has no 'environ' member (no-member)
__________________________ [pylint] tests/test_git.py __________________________
E:210,88: Module 'os' has no 'environ' member (no-member)
_________________________ [pylint] tests/test_store.py _________________________
E:  1, 0: No name 'path' in module 'os' (no-name-in-module)
E: 46,15: Module 'os' has no 'path' member (no-member)
____________________________ [pylint] marge/git.py _____________________________
E:164,18: Module 'os' has no 'environ' member (no-member)
_______________________ [pylint] marge/trailerfilter.py ________________________
E: 63,56: Module 'os' has no 'environb' member (no-member)
E: 63,15: Module 'os' has no 'environb' member (no-member)