ENH: loosen header matching for Athena vtk files to allow compatibility with single variable 'vtk outputs'

[neutrinoceros]

PR Summary

this is a hotfix to #3424 that was merged slighlty before I could integrate this change required by @jzuhone

[jzuhone]

I assume that the answer test failures are unrelated?

[neutrinoceros]

Yes, they are the exact same that we've been seeing on daily runs for a couple days. See for instance today's logs https://tests.yt-project.org/job/yt_py38_latest_deps/346/

[matthewturk]

@meeseeksdev backport to yt-4.0.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout yt-4.0.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 49dac7e42d29b79d7747ed9741ce3aa616855be6

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am "Backport PR #3490: ENH: loosen header matching for Athena vtk files to allow compatibility with single variable 'vtk outputs'"

4. Push to a named branch :

git push YOURFORK yt-4.0.x:auto-backport-of-pr-3490-on-yt-4.0.x

5. Create a PR against branch yt-4.0.x, I would have named this PR:

"Backport PR #3490 on branch yt-4.0.x (ENH: loosen header matching for Athena vtk files to allow compatibility with single variable 'vtk outputs')"

And apply the correct labels and milestones.

Congratulation you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove Still Needs Manual Backport label once the PR gets merged.

If these instruction are inaccurate, feel free to suggest an improvement.

[neutrinoceros]

@meeseeksdev backport to yt-4.0.x