Run BrowserStack tests on GitHub Actions instead of TravisCI

[jelhan]

All tests except BrowserStack are run on GitHub Actions. Only that one is run on TravisCI as we faced issues when migrating it from TravisCI to GitHub Actions. This has been some time ago and BrowserStack finally added offical actions and documentation: https://www.browserstack.com/docs/automate/selenium/github-actions

At the same time Travis gets unreliable slow. While GitHub Actions are finished after a few minutes, TravisCI is pending for hours.

Seems to be a good time to migrate also these remaining tests to GitHub Actions. 😉