Github workflow tests should test all python versions in use in the organization

For instance, in kostra-kommregn we used a matrix to define all python versions that whould be tested: https://github.com/statisticsnorway/kostra-kommregn/blob/dev/.github/workflows/tests.yml

althou we soon only use python 3.13, but we might in the future offer multiple options on this like we have up until now (3.11 and 3.12 in cloud, and 3.10 on-premis)