Fixed test failures on msys. Implemented by Paulo Custodio. GH #116.
When running under GitHub Actions in --check-only mode, linting failures
will now emit GitHub annotations
(https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#example-creating-an-annotation-for-an-error). Implemented
by Pavel Dostál. GH #120.