Run python 3.11 in CI

[cc-a]

We've swapped to developing primarily against Python 3.10 but it's a good idea to future proof and make sure we also worked with 3.11. This implies we should have CI run against 3.11 but in line with our group policy of minimising actions usage this should be less frequent then on every pull request. We could run on a schedule or adopt a more formal release model with associated CI.