Don't augment difficulty of children jobs
Some easy jobs have unexpected high difficulties because of that

![image](https://github.com/huggingface/datasets-server/assets/42851186/4c905bc0-f671-4c11-97b3-3f0c1ec10cb2)

Don't augment difficulty of children jobs: Some easy jobs have unexpected high difficulties because of that

![image](https://github.com/huggingface/datasets-server/assets/42851186/4c905bc0-f671-4c11-97b3-3f0c1ec10cb2)
