Run tests against M1 macOS runner

Github now has M1 runners for open source projects. https://github.blog/changelog/2024-01-30-github-actions-introducing-the-new-m1-macos-runner-available-to-open-source/

We should include it in our CI tests, once we can pass the tests.

It remains a question whether we still run tests against x86_64 macOS.