xmlsecurity: ignore elements in ds:Object that aren't signed

xmlsecurity: ignore elements in ds:Object that aren't signed

Change-Id: I2e4411f0907b89e7ad6e0185cee8f12b600515e8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/111253
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@allotropia.de>
(cherry picked from commit 2bfa00e6bf4b2a310a8b8f5060acec85b5f7a3ce)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/111909
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Gbp-Pq: Name xmlsecurity-ignore-elements-in-ds:Object-that-arent-signed.diff