use pyvista action for headless display in tox

[alessandrofelder]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?

Tests fail weirdly with a display-related thing on Windows CI.

What does this PR do?

Brings the CI set-up of the headless display in line with napari and our napari plugins, ie uses a pyvista GitHub action to set up the headless display.

References

Closes #270

How has this PR been tested?

CI tests now all pass 🎉

Is this a breaking change?

No

Does this PR require an update to the documentation?

No

Checklist:

• [NA] The code has been tested locally
• [NA] Tests have been added to cover all new functionality (unit & integration)
• [NA] The documentation has been updated to reflect any changes
• The code has been formatted with pre-commit

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9a24de2) 67.86% compared to head (d40ab28) 67.94%.
Report is 3 commits behind head on mega-fix.

Additional details and impacted files

@@             Coverage Diff              @@
##           mega-fix     #273      +/-   ##
============================================
+ Coverage     67.86%   67.94%   +0.08%     
============================================
  Files            26       26              
  Lines          1195     1195              
============================================
+ Hits            811      812       +1     
+ Misses          384      383       -1     

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[IgorTatarnikov]

Yay! All tests finally passing on CI 🎉