Test md5 mismatch on Python 3

[crackcomm]

Tests fail with python 3.

$ dune runtest
        bash alias tests/runtest (exit 2)
(cd _build/default/tests && /bin/bash -e -u -o pipefail -c ./test.exe)
Running: python3 -c 'import numpy as np
arr = np.array([ [ 843124160., 305941280., 741140288. ], [ 531715328., 304366752., 573273728. ] ])
np.save("ptest_g.npy", arr.astype("f4"))'

test_g.npy 09823d7cdfe3688f0032c01a207e5bb0 de364fc012daa8645c888b985f16fe99