Intermittent failure: `Test_Client_InsertNotificationsAreDeduplicatedAndDebounced`

Start with Test_Client_InsertNotificationsAreDeduplicatedAndDebounced in client_test.go, especially the failure around lines 6289 and 6350. Run go test ./... -race -timeout 2m and use the linked CI run to compare the intermittent behavior. Done means the test no longer receives an insert notification while it should be debounced.

Intermittent failure in Test_Client_InsertNotificationsAreDeduplicatedAndDebounced.

Sample run:
https://github.com/riverqueue/river/actions/runs/18163358692/job/51699168994?pr=1049

cd /home/runner/work/river/river && go test ./... -race -timeout 2m
--- FAIL: Test_Client_InsertNotificationsAreDeduplicatedAndDebounced (2.80s)
    client_test.go:6289: Reusing idle postgres schema "river_2025_10_01t13_15_00_schema_03" [user facing: "river_2025_10_01t13_15_00_schema_03"] after cleaning in 744.730859ms [4 generated] [3 reused]
    logger.go:256: time=2025-10-01T13:15:01.890Z level=INFO msg="River client started" client_id=runnervm3ublj_2025_10_01T13_15_01_338625
    logger.go:256: time=2025-10-01T13:15:01.890Z level=INFO msg="inserting queue1 job"
    logger.go:256: time=2025-10-01T13:15:01.979Z level=INFO msg="received notification" topic=river_insert payload="{\"queue\": \"queue1\"}"
    logger.go:256: time=2025-10-01T13:15:01.979Z level=INFO msg="inserting queue1 job"
    logger.go:256: time=2025-10-01T13:15:02.043Z level=INFO msg="inserting queue1 job"
    logger.go:256: time=2025-10-01T13:15:02.140Z level=INFO msg="inserting queue1 job"
    logger.go:256: time=2025-10-01T13:15:02.279Z level=INFO msg="inserting queue1 job"
    logger.go:256: time=2025-10-01T13:15:02.903Z level=INFO msg="inserting queue1 job"
    logger.go:256: time=2025-10-01T13:15:02.905Z level=INFO msg="received notification" topic=river_insert payload="{\"queue\": \"queue1\"}"
    client_test.go:6350: received insert notification when it should have been debounced {topic:river_insert payload:{Queue:queue1}}
    logger.go:256: time=2025-10-01T13:15:03.394Z level=INFO msg="River client stopped" client_id=runnervm3ublj_2025_10_01T13_15_01_338625
    riverdbtest.go:289: Checked in postgres schema "river_2025_10_01t13_15_00_schema_03"; 1 idle schema(s) [5 generated] [4 reused]
FAIL
FAIL	github.com/riverqueue/river	27.292s