[Docs]: Child Context docs incorrectly refers to Parallel

[yaythomas]

Issue

The code sample here will run serially.

Page/Location

https://github.com/aws/aws-durable-execution-sdk-python/blob/main/docs/core/child-contexts.md#parallel-child-contexts

Suggested Fix

No response

[leandrodamascena]

I'll fix tomorrow.