Fix `itkwidgets` in the MICCAI23 notebook

[denbonte]

Fix the dark halo around the segmentation masks by setting:

v = view(label_image=data_im)
v.set_label_image_weights([0,1])

This should assign a non-zero weight to all the labels except the background.

See: InsightSoftwareConsortium/itkwidgets#682