Fix red develop 3e6be7706080

The merge lane found `develop` red at `3e6be7706080aa76146dab74b6e95b7f7faccd86` on its own: no queued PR merges until it is fixed. Failing (tests and gate stages): - `tests/test_groups_api.py::test_a_rejected_create_is_recorded_with_its_refusing_status` - `api-unit-dc-test` The whole gate log: artifact `8607` on lane task 9148. Make `develop` pass its full gate again. Open a PR as usual: the merge lane merges a PR that fixes some of these and adds no failure even while `develop` is red.

Updated stale test_groups_api refused-create test to the new 4xx refusal-detail capture (from 4db455f96). Groups suite 42 passed, quick gate green; PR #6679 queued in merge lane. Memory: none applied.