flake: coderd/database/dbpurge TestPurge - bad connection

[deansheather]

Seen here: https://github.com/coder/coder/actions/runs/16993368256/job/48178044395#step:15:551

=== Failed
=== FAIL: coderd/database/dbpurge TestPurge (0.10s)
    mock.go:448: Mock Clock - Trap Now(..., [])
    mock.go:448: Mock Clock - Trap Ticker.Stop(..., [])
    mock.go:448: Mock Clock - Trap Ticker.Reset(..., [])
    t.go:106: 2025-08-15 15:34:21.339 [debu]  pubsub: pubsub dialing postgres  network=tcp  address=127.0.0.1:5432  timeout_ms=0
    t.go:106: 2025-08-15 15:34:21.340 [debu]  pubsub: pubsub postgres TCP connection established  network=tcp  address=127.0.0.1:5432  timeout_ms=0  elapsed_ms=0
    t.go:106: 2025-08-15 15:34:21.342 [debu]  pubsub: pubsub connected to postgres
    t.go:106: 2025-08-15 15:34:21.342 [debu]  pubsub: pubsub has started
    mock.go:202: Mock Clock - NewTicker(10m0s, []) call, matched 0 traps
    mock.go:202: Mock Clock - Now([]) call, matched 1 traps
    mock.go:202: Mock Clock - Since(2024-01-01 00:00:00 +0000 UTC, []) call, matched 0 traps
    t.go:106: 2025-08-15 15:34:21.358 [debu]  purged old database entries  duration=0s
    mock.go:202: Mock Clock - Ticker.Reset(10m0s, []) call, matched 1 traps
    mock.go:357: Mock Clock - AdvanceNext()
    mock.go:202: Mock Clock - Ticker.Stop([]) call, matched 1 traps
    t.go:115: 2025-08-15 15:34:21.360 [erro]  failed to purge old database entries ...
        error= execute transaction:
                   github.com/coder/coder/v2/coderd/database.(*sqlQuerier).runTx
                       /home/runner/work/coder/coder/coderd/database/db.go:213
                 - failed to delete old workspace agent logs:
                   github.com/coder/coder/v2/coderd/database/dbpurge.New.func1.1
                       /home/runner/work/coder/coder/coderd/database/dbpurge/dbpurge.go:60
                 - driver: bad connection
         *** slogtest: log detected at level ERROR; TEST FAILURE ***
    mock.go:202: Mock Clock - Ticker.Reset(10m0s, []) call, matched 0 traps
    mock.go:202: Mock Clock - Ticker.Stop([]) call, matched 0 traps
    t.go:106: 2025-08-15 15:34:21.360 [info]  pubsub: pubsub is closing
    t.go:106: 2025-08-15 15:34:21.360 [info]  pubsub: pubsub listen stopped receiving notify
    t.go:106: 2025-08-15 15:34:21.361 [debu]  pubsub: pubsub closed
    mock.go:477: Mock Clock - test cleanup; will no longer log clock events