I have made the changes I suggested (though correctly...), but ultimately we need to create our own Docker image suitable for running these tests.

So for now, I'm proposing in my PR to make most of the change, as well as a few other Pipelines/test-related improvements, but to leave this open in case someone wants to come in later with a suitable image. At that point, the only change necessary to enable the tests will be to add a "posix_deps_yum.sh" script, update the image name/tag and change the manylinux variable to 'true'.

PR 11493 also fixes a missing LICENSE.txt file in the app store package, which was causing an idlelib test to fail as the fallback text only has one line. *Way* too obscure a failure for my liking, but at least we had a test there, so thanks, Terry :)