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

[kandersolar]

This test is not asserting what it should be:

pvlib-python/pvlib/tests/test_irradiance.py

Lines 133 to 136 in bdbaf4c

	def test_get_ground_diffuse_albedo_0(irrad_data):
	ground_irrad = irradiance.get_ground_diffuse(
	40, irrad_data['ghi'], albedo=0)
	assert 0 == ground_irrad.all()

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!