shogun: disable broken test

Shogun has been broken for a while [0].

Looks like the latest update to openblas, by f07a0615ea8 (openblas:
0.3.20 -> 0.3.21, 2022-08-10), broke the `libshogun-mathematics_lapack`
example. It calculates the eigenvectors for a matrix, but the assertions
now fail:

compute_eigenvectors
A=[
[ -0.500000000000000111, 0.707106781186547351, 0.5],
[ 0.707106781186547351, 1.04083408558608426e-16, 0.707106781186547129],
[ -0.499999999999999722, -0.707106781186547462, 0.5]
]
eigenvalues=[-1.41421356237309492,1.04083408558608426e-17,1.41421356237309492]
terminate called after throwing an instance of 'shogun::ShogunException'

The darwin build output shows a bit more detail:

assertion is_equal(A(0,0), 0.5, eps) failed in void test_ev()
file /tmp/nix-build-shogun-6.1.4.drv-0/source/examples/undocumented/libshogun/mathematics_lapack.cpp
line 49

Disable the test to fix the build, although the results seem "correct".
It appears that openblas now calculates values with slightly less
precision, thus the assertion fails due to the expected epsilon.

[0]: https://hydra.nixos.org/build/194671473

pkgs/applications/science/machine-learning/shogun/default.nix

···
     excludeTestsRegex = lib.concatStringsSep "|" [
       # sporadic segfault
       "TrainedModelSerialization"
+      # broken by openblas 0.3.21
+      "mathematics_lapack"
       # these take too long on CI
       "evaluation_cross_validation"
       "modelselection_combined_kernel"