`test_irradiance.py::test_get_ground_diffuse_albedo_0` test assertion is incorrect

[kandersolar]

This test is not asserting what it should be:

https://github.com/pvlib/pvlib-python/blob/bdbaf4c238ce2b373d04af48193b14659662cef1/pvlib/tests/test_irradiance.py#L133-L136

In effect, this is asserting that there is at least one zero in ground_irrad. I assume the intent of the test is to assert that ground_irrad contains all zeros. The fix is easy, just edit line 136 to be assert (0 == ground_irrad).all().

PRs welcome, especially from new contributors!