Reduce unit test data likelihood of crashing

[garrettwrong]

Some items queried during the unit tests are abusively reaching out and we are deservingly getting throttled, resulting in test failures.

ERROR tests/test_image.py::testMultiDimGets[dtype=<class ‘numpy.float32’>-parity=0] - requests.exceptions.HTTPError: 429 Client Error: Too Many Requests for url: https://raw.githubusercontent.com/scipy/dataset-face/main/face.dat

In this case its

from scipy.datasets import face

Convert to use a different image or if there is something special about the scipy one, cache it outside the tests.

I haven't looked if there are others, but I've hit this one too many times now.