fix coverage drop

Author: kandersolar

pvlib/tests/test_pvsystem.py

@@ -1814,10 +1814,16 @@ def test_PVSystem_multi_array_attributes(attr):
     with pytest.raises(AttributeError):
         getattr(system, attr)
 
+    with pytest.raises(AttributeError):
+        setattr(system, attr, 'dummy')
+
     system = pvsystem.PVSystem()
     with pytest.warns(pvlibDeprecationWarning):
         getattr(system, attr)
 
+    with pytest.warns(pvlibDeprecationWarning):
+        setattr(system, attr, 'dummy')
+
 
 def test_PVSystem___repr__():
     system = pvsystem.PVSystem(