Update hyperparameter_search.py

[pacman100]

What does this PR do?

1. PR Refactor hyperparameter search backends #24384 results in many tests failing related to HP Search. https://huggingface.slack.com/archives/C02CH2YP4EQ/p1687823783572709
2. Error being tests/deepspeed/test_deepspeed.py::TrainerIntegrationDeepSpeed::test_hyperparameter_search (line 122) TypeError: is_available() missing 1 required positional argument: 'self' when default_hp_search_backend is called.
3. This PR fixes it.

Tested this via:

export CUDA_VISIBLE_DEVICES="0"
export RUN_SLOW="yes"
export LOGLEVEL=INFO

cd transformers

pytest -sv tests/deepspeed/test_deepspeed.py::TrainerIntegrationDeepSpeed::test_hyperparameter_search

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Thanks for the fix! Left a small comment.

[sgugger]

Thanks for iterating!

[ydshieh]

Thank you again.

For the scope (the goal) of this PR (to fix test failure), it's good to be merged.

I would say the other methods in those backend classes could (or should better) be static, but no need to touch them in this PR.