Failed to create a new worker

See https://redmine.teklia.com/issues/8367 for report:

STR:

• make stack on backend
• Create worker button
• fill anything
• click Create
• Get Backend error about repository_url

  File "/home/yschneider/dev/arkindex/backend/arkindex/process/serializers/workers.py", line 91, in create
    repository_url=validated_data["repository_url"],
KeyError: 'repository_url'

Does not happen when I use .get(...) here