Flakey unoconv test

[Yelinz]

See for example https://github.com/adfinis/document-merge-service/actions/runs/9953266814/job/27496796865

Might be good to evaluate #528 .

See https://www.github.com/unoconv/unoconv/issues/591 for upstream tracking

[derrabauke]

Still an issue. See: https://github.com/adfinis/document-merge-service/actions/runs/15091266700/attempts/1