Port from travis to github workflow.

[stuaxo]

Hi, Here is a bit of a go at porting travis to a github action. It was a bit more painful than I expected.

This sticks with old-ish dependencies for now (though some are newer).

• Redis changed zadd signature slightly.
• setup.py test requires went away, so had to use an extra.

Various bits still use old deps, so they can keep working - I think everything wants to move to pyproject.toml (certainly some of the newer tox bits).

Bumping everything to newer versions could be abother task.

I have no idea if the deploy task works.