Troubleshooting the Relationship calculator (or the localization) is a bit beyond my Pyrhon skillset.
There is a difference in an empty line (added by Black formatting) and removal of spaces on an empty line (removed by Black). Those are the two things Black is pointing out at the moment. While you may not see a visual diff, uploading the output of Black 24.4.2 should make the check pass.
The relationship calculation is beyond my limited knowledge.
Filed a new Feature request:
0013526 : Spouses siblings are not listed as “in-laws” in the Kinship Report
However, this seems to have been the originally intended scope. The included people were only the direct ancestors and descendants. The sideways expansion was limited to siblings of the center person and spouses of anyone in the list.
It does not include cousins, niblings or spouse immediate family.