Get pytest-error-for-skips from PyPI

[chrisburr]

I wasn't expecting my PR to fix pytest-error-for-skips to be accepted as it hadn't been updated in years but it has been so we can now get it from PyPI.

Also skips test_issue390 if pandas is unavailable.

[jpivarski]

Oh I see what this is now. When @reikdas pointed me to that pip install of a GitHub repo, it looked very fragile to me. I must have accepted it without noticing. I also didn't understand the purpose of it, but now that I see it here, I see why you did that. I'm definitely in favor of more explicit (and reported) skipping.

I'll merge that's if you're done. Just give me confirmation.

[chrisburr]

Yeah, I'm very happy the maintainer jumped in to make a new release as it seems like a useful little package. I'd normally say it was too small to justify a dependency but as it's only for the CI I think it makes sense.

I'm done so go ahead and merge!