Add .github/workflows/main.yml to run python2 pylint --py3k checks

[bernhardkaindl]

This enables pylint's checks to detect Python2 to Python3 migration problems in CI using python2 pylint's specific python3 migration checks.

Note: Those had been deemed obsolete and removed in the later python3 pylint, so they only exist in the specific older pylint which runs on and still supports python2 code.

Also add the needed .pylintrc for python2 pylint --py3k checks.