TST: suppress 1485 warnings issued by xml parser
So we don't have to scroll through tons of 

```
pandas/tests/io/excel/test_xlrd.py::test_excel_table_sheet_by_index[.xlsm]
  /usr/local/lib/python3.7/site-packages/xlrd/xlsx.py:312: PendingDeprecationWarning: This method will be removed in future versions.  Use 'tree.iter()' or 'list(tree.iter())' instead.
    for elem in self.tree.iter() if Element_has_iter else self.tree.getiterator():
```