Add comment for the need of type: ignore

Author: makbigc

pandas/core/indexes/datetimelike.py

@@ -134,7 +134,7 @@ def values(self) -> np.ndarray:
         # Note: PeriodArray overrides this to return an ndarray of objects.
         return self._data._data
 
-    @property  # type: ignore
+    @property  # type: ignore # https://github.com/python/mypy/issues/1362
     @Appender(DatetimeLikeArrayMixin.asi8.__doc__)
     def asi8(self):
         return self._data.asi8