[Bug] Using TaskGroup for child workflow execution does not correctly detect failure #1020

# workflows.py
import asyncio
from datetime import timedelta
from typing import List

from temporalio import workflow
from temporalio.common import RetryPolicy

# Import activity, passing it through the sandbox without reloading the module
with workflow.unsafe.imports_passed_through():
    from activities import say_hello


@workflow.defn
class SayHello:
    @workflow.run
    async def run(self, name: str) -> str:
        return await workflow.execute_activity(
            say_hello, name, start_to_close_timeout=timedelta(seconds=5), retry_policy=RetryPolicy(maximum_attempts=3)
        )


@workflow.defn
class MasterWorkflow:
    @workflow.run
    async def run(self, names: List[str]) -> List[str]:
        tasks: List[asyncio.Task[str]] = []
        async with asyncio.TaskGroup() as tg:
            for name in names:
                tasks.append(
                    tg.create_task(
                        workflow.execute_child_workflow(
                            SayHello.run, name, id=f"say-hello-{name}", retry_policy=RetryPolicy(maximum_attempts=1)
                        )
                    )
                )

        greetings = [task.result() for task in tasks]

        return greetings

# activities.py
from temporalio import activity


@activity.defn
async def say_hello(name: str) -> str:
    if name == "fail":
        raise Exception("Uh-oh")
    return f"Hello, {name}!"

# run_workflow.py
import asyncio

from temporalio.client import Client

from run_worker import MasterWorkflow


async def main():
    # Create client connected to server at the given address
    client = await Client.connect("localhost:7233")

    # Execute a workflow
    result = await client.execute_workflow(
        MasterWorkflow.run, ["ok", "fail", "okay", "cool"], id="master-workflow", task_queue="hello-task-queue"
    )

    print(f"Result: {result}")


if __name__ == "__main__":
    asyncio.run(main())

# run_worker.py
import asyncio

from temporalio.client import Client
from temporalio.worker import Worker

from activities import say_hello
from workflows import MasterWorkflow, SayHello


async def main():
    client = await Client.connect("localhost:7233", namespace="default")
    # Run the worker
    worker = Worker(
        client, task_queue="hello-task-queue", workflows=[MasterWorkflow, SayHello], activities=[say_hello]
    )
    await worker.run()


if __name__ == "__main__":
    asyncio.run(main())