Fix red develop 9ec0af9d0511

The merge lane found `develop` red at `9ec0af9d0511409680e22933b2f660f7d50a545e` on its own: no queued PR merges until it is fixed. Failing (tests and gate stages): - `tests/test_credential_key_rotation.py::test_legacy_unprefixed_tier1_ciphertext_opens_under_a_rotated_ring` - `tests/test_credential_key_rotation.py::test_reseal_moves_both_tiers_and_a_row_sealed_before_rotation_still_decrypts` - `tests/test_credential_key_rotation.py::test_the_current_aes_key_listed_as_previous_is_dropped` - `tests/test_credential_key_rotation.py::test_previous_kms_keys_need_a_kms_current_key` - `tests/test_credential_key_rotation.py::test_previous_kms_keys_are_unwrap_only_providers_without_the_current_one` - `api-unit-dc-test` The whole gate log: artifact `12174` on lane task 11288. 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.

Superseded: Task 11288 (PR #7352, a7099eb2a) already fixed the key-rotation failures with the same fixture. On develop the suite is 10 passed; at the red sha, 5 failed. Closed PR #7353 (it duplicated the fixture after the lane merge). Memory: none applied.