TST: Upcoming dependency test failures

[github-actions]

The weekly build with future dependencies has failed. Check the logs
https://github.com/yt-project/yt/actions/runs/15723144292

[neutrinoceros]

The failure is that pytest dev changed behavior on raise unittest.SkipTest in pytest-dev/pytest#13528

The reason we use unittest.SkipTest is that it allows us to transition from nose to pytest, specifically because it (used to) worked with both frameworks, but I had no idea that pytest did it only to support nose...
The easiest fix would be to ask for a revert upstream, but there might be a better way to fix on our side. I'll take a quick look.