Install also gmsh and python-gmsh conda packages.

[ci] Run jupyter tests in regular (osmesa) container.

Rendering backend can be set via:

    import pyvista as pv

    pv.set_jupyter_backend('ipyvtklink') # default
    pv.set_jupyter_backend('pythreejs')
    pv.set_jupyter_backend('static')

Is currently not supported on the deployed user container.