CI pipelines for Windows and MacOS

[aucampia]

Currently the CI only runs for linux, but the result is that things have fallen into disrepair for windows and to a much lesser extent MacOS. It would be nice if we could run CI on these platforms also before merging patches.

Currently GitHub actions does provide windows and macos runners and I have done some work to set it up here: aucampia/rdflib@iwana-20211018T2122-pytest...iwana-20211113T1312-github-actions

I have not set it up for Windows yet, but this is mainly because windows is still having some weird issues which I'm independently debugging.

We can maybe start by running this in parallel to drone, I think drone can maybe test windows also but I don't think it can do macos.

Any input on this would be welcome.

[aucampia]

@nicholascar I made two PRs:

• Add GitHub actions workflow for validation #1461
• Make the test pass on windows #1478

Merging #1461 won't really help much until #1478 is merged, and you will also need to enable github actions on this project/organization for it.