This repository includes a Demo Extension for TYPO3 CMS and a fully functional GitHub Actions workflow configuration to execute Unit-, Functional- and Acceptance-Tests
I have written a detailled blogpost about how to setup the GitHub Actions workflow at https://www.derhansen.de/2020/05/typo3-extension-testing-with-github-actions.html
The blogpost explains some important steps you need to be aware of when using GitHub Actions for PHP applications with Functional- or Codeception Acceptance-Tests, so make sure you at least have a quick look at the "Good to know"-section at the end of the article.