Fix issues in volatile deps

Found these while testing connections.xml

openpyxl/volatile/volatile_deps.py Excel cares about the order of these elements and would say the file was mangled if they were out of order.

openpyxl/workbook/tests/test_writer.py Pretty straightforward. Test had been copied from metadata but hadn't been renamed.

openpyxl/doc/conf.py Don't need docs generated for the tests.

--HG-- branch : 3.2