CI: execute tests with GH Actions

[matttbe]

Cirrus CI has some limitations now.

An alternative is to use GH Actions.

I tried it and it takes:

• 'normal' mode: ~1h (compilation and tests)
• 'debug' mode: ~6h (and many issues)

But we are not limited apparently.

We can keep Cirrus CI for the debug mode for the moment, but it means 2 reports.

Alternative: use a self hosted runner.

We should publish the results somewhere:

• KCIDB
• https://github.com/marketplace/actions/test-reporter
• https://github.com/marketplace/actions/publish-test-results
• https://github.com/marketplace/actions/junit-report-action
• (...)

[matttbe]

We can close this ticket:

• tracking is handled in #473
• self hosted runners is handled in #474