Fix flaky test: TestHistoryModifierTask/Normal_execution_with_multiple_logs_and_groups

```
--- FAIL: TestHistoryModifierTask (0.00s)
    --- FAIL: TestHistoryModifierTask/Normal_execution_with_multiple_logs_and_groups (0.00s)
        historymodifier_task_test.go:163: expected 3 resources, but got 2
```

https://github.com/GoogleCloudPlatform/khi/actions/runs/18361255500/job/52347998287