Change error msg in test_sub_dti_dti

Author: makbigc

pandas/tests/arithmetic/test_datetime64.py

@@ -2091,7 +2091,7 @@ def test_sub_dti_dti(self):
         # different length raises ValueError
         dti1 = date_range('20130101', periods=3)
         dti2 = date_range('20130101', periods=4)
-        msg = 'cannot add indices of unequal length'
+        msg = 'Lengths must match to compare'
         with pytest.raises(ValueError, match=msg):
             dti1 - dti2