Fix flaky test tests/token_billing/test_routes.py::test_a_credit_with_no_reason_is_refused[

The merge lane saw `tests/token_billing/test_routes.py::test_a_credit_with_no_reason_is_refused[` fail and then pass on a rerun of the same tree. - Test: `tests/token_billing/test_routes.py::test_a_credit_with_no_reason_is_refused[` - Tree: `336500b9600a16cbb307ba31a69997424d5b7820` - Lane task: 9614 - Flake record: 01a16cd3-d614-7c1c-b89e-74003818fa9b Make it deterministic; do not delete it unless it tests nothing. - Also flaky, same file: `tests/token_billing/test_routes.py::test_off_the_plan_reads_own_and_refuses_buying_credit_but_not_a_refund` (tree `336500b9600a16cbb307ba31a69997424d5b7820`, lane task 9614, flake record 01a16cd3-d8e8-7d42-a5d6-70ab397a4fa2)

Duplicate: the test_routes flakes were collateral from a stopped shared TestClient portal on gw1. Already fixed on develop by Task 9617 (guard, PR #6804) and Task 9620 (culprit). Reproduced, then verified clean on develop. No PR. Memory: none applied.