#1448 Hotfix/GitHub actions (state: open)

Description

This changes the build flow from travis-ci to github-actions.

The change is necessary, as travis discontinued the open source minutes with the migration from https://travis-ci.org/ to https://travis-ci.com/

Checklist

• [X] Read and understood the CONTRIBUTING guidelines
• [X] All tests passing
• [X] Checked the changes with phpcq and introduced no new issues