Bugfix/fix GitHub actions

[gkalab]

This pull request fixes the continuous integration workflow (github action). I re-enabled the workflow for one run. You can see the results here: https://github.com/JohanSjoblom/picochess/actions/runs/19533218530

The main change is the Python version used for the actions and I changed the Ubuntu version to a specific, slightly older version to fix the bluepy compile issue.
All the failing tests are fixed and some of the lint and type errors as well.
There are still some warnings/errors left but the actions are running again.

Let me know if you would like me to create an issue first and rename the branch or how to go about naming branches in the future.

[gkalab]

To run the tests locally in my dev environment, I used the following commands:

tox -e unit
tox -e lint
tox -e static

[JohanSjoblom]

Nice work. Fixing the unit tests was on my todo list, so greatly appreciated.

I have no strong opinion on naming branches. If they come from issues I usually keep the issue number there, if they are fixes I think all hotfix/x or fix/x or bugfix/x like you did is more than fine.
I think I need to promote you to developer... I will do that as well as merging this.