Rethink use-xvb option in the test action

[niksirbi]

The test action currently accepts an optional "use-xvfb" argument, which in turn uses a headless-gui action (with a specific commit hash).

- name: Run tests with XVFB
      if: ${{ matrix.use-xvfb }}
      # SHA corresponds to v1.1 release
      uses: aganders3/headless-gui@f85dd6316993505dfc5f21839d520ae440c84816
      with:
        run: tox ${{ inputs.tox-args }}

I'm not sure why this hash is needed, or if we can simply switch to v2 of that action.

We could also consider switching to the https://github.com/pyvista/setup-headless-display-action, which I think does the same (or similar) thing. @IgorTatarnikov has reported that it does the trick for brainglobe-stitch. We would have to compare that one to a more recent version of aganders3/headless-gui and check which ones best serves our needs.

[alessandrofelder]

AFAIK we now consistently use the pyvista alternative throughout BrainGlobe so I think switching to that would make sense (see e.g https://github.com/brainglobe/brainrender-napari/blob/d93447b5d1f5592aece2b39780442e7acbb7854f/.github/workflows/test_and_deploy.yml#L49)