silence tests on Windows

[olivroy]

Summary

Since the logs are noisy due to file not found.

Now, the only remaining failures in tests is #1481, which is genuine, but with this PR, it works better to run tests locally on windows.

The image snapshot error is annoying too, so I skipped it on windows. I opened r-lib/waldo#191 for options.

Basically, render related warnings are silenced on Windows. I would recommend you investigate a bit more if you have time. But gt is generally working well. I think it is safe to ignore these warnings when running tests locally.

It will make contributing in the future a bit easier!

These are mostly in .Rbuildignore, so won't change much. They are only run on CI on Ubuntu. So the only way to get that is locally on Windows.

I also took advantage to do some test refactoring to make the warning testing a bit more explicit

Related GitHub Issues and PRs

Checklist

• I understand and agree to the Code of Conduct.
• I have listed any major changes in the NEWS.
• I have added testthat unit tests to tests/testthat for any new functionality.

[rich-iannone]

LGTM!