Add tests for submission meta attributes pipeline.

- [ ] Add test to ensure that from a `challenge_config`, the attributes are being validated correctly and stored in the model field `submission_meta_attributes_scehma`.

Start by locating the challenge_config handling and the model field submission_meta_attributes_scehma, then inspect nearby tests for the existing validation and persistence patterns. Add coverage showing that attributes from a challenge_config are validated correctly and stored in that field; the issue is complete when those behaviors are verified by the test suite.

Written by the indexing model from the issue text.