[Bug] bugs/go/child_workflow_cancel_panic flaky

As seen in https://github.com/temporalio/features/actions/runs/5954797392/job/16152095861?pr=329#step:9:230

this feature sometimes flakes out. Investigate and fix.

In case link goes stale:

2023-08-23T17:59:49.164Z	DEBUG	harness/log.go:44	Checking history	{"Feature": "bugs/go/child_workflow_cancel_panic"}
2023-08-23T17:59:49.164Z	DEBUG	harness/log.go:44	Checking current execution replay	{"Feature": "bugs/go/child_workflow_cancel_panic"}
2023-08-23T17:59:49.164Z	INFO	harness/log.go:48	Task processing failed with error	{"Namespace": "features-ns-a7611eeb-a29d-4dd7-ba1f-75df46a4f5c6", "TaskQueue": "features-bugs/go/child_workflow_cancel_panic-d884c0ea-35f3-422b-9e2c-e1daf9d47869", "WorkerID": "4782@fv-az446-536@", "WorkerType": "WorkflowWorker", "Error": "Workflow task not found."}
2023-08-23T17:59:49.171Z	INFO	harness/log.go:48	Stopped Worker	{"Namespace": "features-ns-a7611eeb-a29d-4dd7-ba1f-75df46a4f5c6", "TaskQueue": "features-bugs/go/child_workflow_cancel_panic-d884c0ea-35f3-422b-9e2c-e1daf9d47869", "WorkerID": "4782@fv-az446-536@"}
2023/08/23 17:59:49 INFO  No DataConverter configured for temporal worker. Use default one.
2023/08/23 17:59:49 ERROR Workflow panic WorkflowType Sleep WorkflowID ReplayId RunID 304a6e40-13ea-4f85-bf9f-f6757d5a69e3 Attempt 1 Error nondeterministic workflow: extra replay command for CancelTimer: (TimerId:5)
2023-08-23T17:59:49.171Z	ERROR	harness/log.go:56	Feature failed	{"Feature": "bugs/go/child_workflow_cancel_panic", "error": "failed replaying current execution: nondeterministic workflow: extra replay command for CancelTimer: (TimerId:5)"}

Start with the bugs/go/child_workflow_cancel_panic feature and reproduce the flaky run linked in the issue. Review the harness output in harness/log.go, especially the task-processing and feature-failure paths, alongside the nondeterministic CancelTimer error. Done means the feature no longer flakes and the current execution replays successfully.