Bump Python version for tutorials

[glatterf42]

We're seeing the same error in our CI again as we did previously when GitHub runner-images first changed ubuntu-latest to Ubuntu 24.04. They are rolling out the same change again now. However, we have adopted Python 3.13 in the meantime and in the ixmp test suite, this seems to work, while Python 3.12 produces the same error with Ubuntu 24.04. 3.11 works with that image, too, so the error might be specific to Python 3.12. Thus, this PR bumps the Python version we use for the tutorial tests in hopes of enabling them to run again on ubuntu-latest.

If this works, we might be able to adjust the ixmp test suite to only use Ubuntu 22.04 with Python 3.12.

See IRkernel/IRkernel#747 and r-lib/actions#932 for the issues I opened about this back then.

How to review

• Read the diff and note that the CI checks all pass.

PR checklist

• Continuous integration checks all ✅
• Update test suite; coverage checks both ✅
• [ ] Add, expand, or update documentation. Just CI bump.
• [ ] Update release notes. Just CI bump.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.7%. Comparing base (5c0b44f) to head (57b6868).

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #898     +/-   ##
=======================================
+ Coverage   95.6%   95.7%   +0.1%     
=======================================
  Files         46      45      -1     
  Lines       4337    4315     -22     
=======================================
- Hits        4147    4131     -16     
+ Misses       190     184      -6     

see 3 files with indirect coverage changes

[glatterf42]

All tutorial tests are now failing, but notably after the step that is failing in our CI suite. This seems to confirm that using Python 3.13 with Ubuntu 24.04 resolves that issue :)

The reason the tests are still failing is likely that pyam doesn't officially support Python 3.13 yet, which it can't until ixmp4 does. For ixmp4, all that is needed for that is a new release, which I will ask about right away. I even prepared a PR for pyam already.

[glatterf42]

I have now also opened actions/runner-images#11137 to see if this bug can be resolved on the runner-image level.