GitHub Action to lint Python code

[cclauss]

GHA may be a bit easier to work with than AppVeyor

Test results: https://github.com/cclauss/multibuild/actions

[multibuilder]

I created a test.yml action as a base for running tests. I don't think we want to begin with a linting task, that seems a bit advanced for now.

[cclauss]

It seems a bit advanced.

The tests pass. ;-) https://github.com/cclauss/multibuild/actions

[mattip]

@matthew-brett any thoughts about adding linting?

[cclauss]

Status?

[mattip]

The CI run seems very fast, let's put this in. If it gets too noisy we can adjust it.