ci: switch Travis to Github Actions

[agnes512]

Connects to https://github.com/strongloop/loopback-next/issues/7054

Checklist

👉 Read and sign the CLA (Contributor License Agreement) 👈

• [ ] npm test passes on your machine
• [ ] New tests added or existing tests modified to cover all changes
• [ ] Code conforms with the style guide
• [ ] Commit messages are following our guidelines

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.