Add GitHub Actions workflow for running validate.py etc

[magnusbaeck]

Description

This repository should have a GitHub Actions workflow that runs validate.py and possibly other relevant scripts to make sure that no blatant errors hit the branch. These tests should preferably be run via tox to make it easy for humans to run the tests locally too.

Motivation

This reduces the risk of errors and/or decreases the verification burden for maintainers.

Exemplification

N/A

Benefits

See motivation above.

Possible Drawbacks

None.

[e-backmark-ericsson]

This sounds like a good idea!