Add/move linting to GH Actions

[helen]

Description of the Change

As advertised - good for annotations and working on consolidating CI into one place.

Alternate Designs

Leaving on Travis.

Benefits

Single interface, more team experience and growing ecosystem.

Possible Drawbacks

Not sure yet, initial run when this PR is opened might tell us some things :)

Verification Process

This is copy-pasted from another working source, I did not try it locally, just going to let it run live since it's a PR.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Also see #215

Changelog Entry

Not really release-relevant