[websitepublisher] Use tar filter to fix sphinx CD
In the sphinx pipelines we use rdfind to de-duplicate data and reduce the data size a lot. This produces symlinks with .. which the very stict "data" filter does not like, the "tar" filter solves that problem and should still be good enough.
See https://invent.kde.org/documentation/docs-kdenlive-org/-/jobs/1579122