Apply suggestions from code review

Co-authored-by: Kevin Anderson <kevin.anderso@gmail.com>

Author: cwhanse

tests/test_pvsystem.py

@@ -509,10 +509,10 @@ def test_PVSystem_faiman_rad_celltemp(mocker):
     temps = 25
     irrads = 1000
     winds = 1
-    out = system.get_cell_temperature(irrads, temps, winds, ir_down=ir_down,
+    out = system.get_cell_temperature(irrads, temps, winds, longwave_down=longwave_down,
                                       model='faiman_rad')
     temperature.faiman_rad.assert_called_once_with(irrads, temps, winds,
-                                                   ir_down, u0, u1,
+                                                   longwave_down, u0, u1,
                                                    sky_view, emissivity)
     assert_allclose(out, 48.6, atol=1e-1)