fdo#54361:Add test case for the chart background

Change-Id: I03f0a45d821b14fe687b3ec7df98f9367adab1f2
Reviewed-on: https://gerrit.libreoffice.org/9978
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>