dedc6768

By: David Nies <david.nies@posteo.de>

Change Python version to 3.13 for the `gi` test

Prior to this change, we used Python 3.14. This caused the whole pytho distribution to be rebuilt, as
well as the `graph-tool` dependency. This takes very long, consumes many CPUs and RAM and ultimately
makes the CI fail.

This change uses python 3.13 which is cached.