TST: Added test for strided inputs in sepfir2d

[Smit-create]

Reference issue

• References: Tackling some sepfir2d improvements rgommers/scipy#43

cc @rgommers

[tylerjereddy]

The MacOS CI failure looks related at least:

=================================== FAILURES ===================================
________________________________ test_sepfir2d _________________________________
scipy/signal/tests/test_bsplines.py:267: in test_sepfir2d
    assert_allclose(signal.sepfir2d(image, filt, filt[::3]), expected)
E   AssertionError: 
E   Not equal to tolerance rtol=1e-07, atol=0
E   
E   Mismatched elements: 2 / 16 (12.5%)
E   Max absolute difference: 31.99999962
E   Max relative difference: 1.02353683

[Smit-create]

Do I need to do something else for MacOS. Locally, running the tests for signal submodule on Linux passes for me:

scipy/signal/tests/test_bsplines.py::test_sepfir2d PASSED                [  0%]
...
============== 2787 passed, 2 skipped, 10475 deselected in 53.99s ==============

[rgommers]

This passes for me on macOS 11 with the conda compilers. The issue may be specific to GCC.

[Smit-create]

Please have a look at this. @rgommers