Fix red develop dbd59a5b262d

The merge lane found `develop` red at `dbd59a5b262db94affd49c2d14501c54f291eefd` on its own: no queued PR merges until it is fixed. Failing (tests and gate stages): - `tests/test_activity_kinds.py::test_the_surviving_sites_are_exactly_the_audited_keep_list` - `api-unit-dc-test` The whole gate log: artifact `9294` on lane task 9577. 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.

Fixed red develop. Task 9568 moved the api_key owner-removal audit write into api_keys._forget, so the activity_kinds keep-list now names _forget. Activity-kinds tests 46/46 and quick gate green. PR #6794 queued in the merge lane. Memory: none applied.