This replicate the existing Azure DevOps workflow, and adds a couple of new
jobs (Python 2.7 on macOS, Python + vanilla Ansible on Linux).
The GitHub Actions use container images hosted on GitHub Container Registry
(GHCR, ghcr.io/mitogen-hq). These images have been copied straight from the
existing Amazon Elastic Cloud Registry (AWS ECR, public.ecr.aws/n5z0e8q9).
A short period of parallel running is planned. Then a second PR will remove
the Azure DevOps workflow.
Alex Willmer