Fix flaky test tests/token_billing/test_bedrock_acp_metering.py::test_the_acp_leg_and_the_legacy_leg_record_the_same_spend

The merge lane saw `tests/token_billing/test_bedrock_acp_metering.py::test_the_acp_leg_and_the_legacy_leg_record_the_same_spend` fail and then pass on a rerun of the same tree. - Test: `tests/token_billing/test_bedrock_acp_metering.py::test_the_acp_leg_and_the_legacy_leg_record_the_same_spend` - Tree: `336500b9600a16cbb307ba31a69997424d5b7820` - Lane task: 9614 - Flake record: 01a16cd3-cdf5-7745-bc2f-e89909331eb9 Make it deterministic; do not delete it unless it tests nothing.

Root cause: test_tenant_receive patched the process-wide clock to inf, killing gw1's session TestClient portals. Task 9620 merged the same fix first (#6802), verified on develop: 4 passed. No PR. Memory: proposed mem-25267.