MAINT: Fix CircleCI

[larsoner]

Will fail until pyvista/pyvista#7746 lands. In the meantime, we should be able to see the improved traceback in the CircleCI output of the touched example (which is failing on main) that takes

    3 vtkPolyData @ mne/conf.py:Resetter.__call__:after:70_fnirs_processing.py:
    list: len=1, 4 referrers: dict/list
    list: len=1, 4 referrers: dict/list
    list: len=1, 4 referrers: dict/list

and makes it a bit more informative:

    3 vtkPolyData @ mne/conf.py:Resetter.__call__:after:70_fnirs_processing.py:
    list[0] with len=1 | 3 referrers: dict['_glyph_geom'] / list[1] / list[743437]
    list[0] with len=1 | 3 referrers: dict['_glyph_geom'] / list[1] / list[743441]
    list[0] with len=1 | 3 referrers: dict['_glyph_geom'] / list[1] / list[743444]

which made it way faster to diagnose than before (I could git grep _glyph_geom and see it had to be a PyVista regression rather than an MNE one).