[trainer / deepspeed] fix hyperparameter_search
This PR:
- fixes `hyperparameter_search` deepspeed config reset fix up that got out of sync with the normal code path
- adds a test so that will not happen in the future.
- adds a new group of pip deps: `deepspeed-testing`

@sgugger 

Fixes: https://github.com/huggingface/transformers/pull/11966#issuecomment-1058493821
_The documentation is not available anymore as the PR was closed or merged._