TST: TestLGMRES on ARM for conda-forge

[tylerjereddy]

This test is causing issues on ARM architecture for conda-forge. Should it be skipped for that arch for now? See here: conda-forge/scipy-feedstock#121 (comment)

=================================== FAILURES ===================================
___________________________ TestLGMRES.test_arnoldi ____________________________
[gw16] linux -- Python 3.8.0 $PREFIX/bin/python

self = <scipy.sparse.linalg.isolve.tests.test_lgmres.TestLGMRES object at 0xffff85668970>

    @pytest.mark.skipif(python_implementation() == 'PyPy',
                        reason="Fails on PyPy CI runs. See #9507")
    def test_arnoldi(self):
        np.random.rand(1234)
    
        A = eye(2000) + rand(2000, 2000, density=5e-4)
        b = np.random.rand(2000)
    
        # The inner arnoldi should be equivalent to gmres
        with suppress_warnings() as sup:
            sup.filter(DeprecationWarning, ".*called without specifying.*")
            x0, flag0 = lgmres(A, b, x0=zeros(A.shape[0]),
                               inner_m=15, maxiter=1)
            x1, flag1 = gmres(A, b, x0=zeros(A.shape[0]),
                              restart=15, maxiter=1)
    
        assert_equal(flag0, 1)
>       assert_equal(flag1, 1)
E       AssertionError: 
E       Items are not equal:
E        ACTUAL: 0
E        DESIRED: 1

A          = <2000x2000 sparse matrix of type '<class 'numpy.float64'>'
	with 4000 stored elements in Compressed Sparse Row format>
b          = array([0.66251662, 0.41577372, 0.78795017, ..., 0.85405312, 0.28446381,
       0.46928199])
flag0      = 1
flag1      = 0
self       = <scipy.sparse.linalg.isolve.tests.test_lgmres.TestLGMRES object at 0xffff85668970>
sup        = <numpy.testing._private.utils.suppress_warnings object at 0xffff85668af0>
x0         = array([0.57539138, 0.34812065, 0.78646772, ..., 0.39001543, 0.28446385,
       0.45351755])
x1         = array([0.57539138, 0.34812065, 0.78646772, ..., 0.39001543, 0.28446385,
       0.45351755])
../_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeh/lib/python3.8/site-packages/scipy/sparse/linalg/isolve/tests/test_lgmres.py:110: AssertionError

It seems we already skip it for PyPy.

[tylerjereddy]

I noted that this test isn't touched by #11181