Test with all supported pythons

[JakubAndrysek]

https://hynek.me/articles/python-github-actions/

Makefile:

# #run python code with array of versions
PY_VERSIONS = 3.8 3.9 3.10 3.11

installDepsAllPy:
    @echo "installing dependencies for all python versions"
    @for version in $(PY_VERSIONS); do \
        echo "installing dependencies for python $$version"; \
        python$$version -m pip install -r requirements.txt; \
    done

runAllPythons:
    @echo "Running mkdocs serve with all python versions"
    @for version in $(PY_VERSIONS); do \
        echo "Running mkdocs serve with python $$version"; \
        python$$version -m mkdocs build; \
    done