CI: Make GitHub Actions builds compatible with Windows

GitHub actions support executing bash script in Windows. But currently, our bash script to setup the environment doesn’t work, because the path to conda is not set correctly for Windows (only for Linux): https://github.com/ibis-project/ibis/blob/master/ci/setup_env.sh#L10 (the conda location is defined in GitHub actions with the env variable $CONDA if I’m not wrong).

We should fix the script so it works on Windows, and then we should add windows-latest to the build of backends that don’t require a docker container: https://github.com/ibis-project/ibis/blob/master/.github/workflows/main.yml#L18

[datapythonista]

so maybe it should be linked to this?

That issue has a Closes #2389, they are linked already. 😃

Not sure if we’ll be able to use a matrix in all cases. If we still want to test mysql/postgres (or other backends) in Windows, I don’t think we can use the same approach. GitHub Actions don’t implement the services (docker containers) in Windows afaik.

[datapythonista]

You could run it in your fork by just opening the PR against your fork master, instead of the main repo master. You can also remove the builds and steps you don’t need if you are going to do lots of tests. But it’s fine to open a normal PR and keep testing here. If you do that you can prefix the title with WIP so we know it’s not yet ready.