Excel expects the group field items to be in ascending order starting
from "<01/02/2010", then "Jan", "Feb", ..., then end with ">01/02/2020".

Change-Id: I29e9b55f43091ed007f59e10dec64f46a37c7d5f
Reviewed-on: https://gerrit.libreoffice.org/70800
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>