This reduces the number of jobs from 48 to 24. The Mitogen part of the test
suite has been parameterized on the Linux container targets to be run against.
Both the Ansible tests & Mitogen tests now use the same source of truth to
control which targets to use: environment variable MITOGEN_TEST_DISTRO_SPECS.
This replaces the two mutually exclusive env vars DISTRO and DISTROS. I've
also removed vestgial traces of an unused env var MITOGEN_TEST_DISTRO.
Parameterization adapted from
https://eli.thegreenplace.net/2014/04/02/dynamically-generating-python-test-cases
refs #1058, #1059
This will allow a single job to be required in the GitHub branch protection
web UI; regardless of which jobs are added to or removed from the matrix of
platform specific, Ansible specific jobs.
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.