Intermittent test failure: `TestDriverRiverPgxV5/JobRetry/UpdatesA_cancelled_JobToBeScheduledImmediately`

[brandur]

Another related to using real clocks for test timing:

--- FAIL: TestDriverRiverPgxV5 (13.25s)
    --- FAIL: TestDriverRiverPgxV5/JobRetry (0.00s)
        --- FAIL: TestDriverRiverPgxV5/JobRetry/UpdatesA_cancelled_JobToBeScheduledImmediately (0.22s)
            riverdrivertest.go:1453: 
                	Error Trace:	/home/runner/work/river/river/internal/riverinternaltest/riverdrivertest/riverdrivertest.go:1453
                	Error:      	Max difference between 2025-03-09 01:48:18.466395912 +0000 UTC and 2025-03-09 01:48:18.249727 +0000 UTC allowed is [10](https://github.com/riverqueue/river/actions/runs/13743615117/job/38435831370?pr=800#step:7:11)0ms, but difference was 216.668912ms
                	Test:       	TestDriverRiverPgxV5/JobRetry/UpdatesA_cancelled_JobToBeScheduledImmediately
        --- FAIL: TestDriverRiverPgxV5/JobRetry/UpdatesA_available_JobToBeScheduledImmediately (0.22s)
            riverdrivertest.go:[14](https://github.com/riverqueue/river/actions/runs/13743615117/job/38435831370?pr=800#step:7:15)53: 
                	Error Trace:	/home/runner/work/river/river/internal/riverinternaltest/riverdrivertest/riverdrivertest.go:1453
                	Error:      	Max difference between 2025-03-09 01:48:18.467961054 +0000 UTC and 2025-03-09 01:48:18.250775 +0000 UTC allowed is 100ms, but difference was 217.186054ms
                	Test:       	TestDriverRiverPgxV5/JobRetry/UpdatesA_available_JobToBeScheduledImmediately
FAIL
FAIL	github.com/riverqueue/river	19.356s

https://github.com/riverqueue/river/actions/runs/13743615117/job/38435831370?pr=800