Replaced deprecated `optuna.suggest_uniform(...)` by `optuna.suggest_float(..., low=..., high=...)`.

Replaced deprecated optuna.suggest_uniform(...) by optuna.suggest_float(..., low=..., high=...).

Description

Replaced deprecated optuna.suggest_uniform(...) by optuna.suggest_float(..., low=..., high=...) in the rl_zoo3/hyperparams_opt.py file.

[x] I have raised an issue to propose this change (required for new features and bug fixes)

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)
[ ] Documentation (update in the documentation)

[x] I've read the CONTRIBUTION guide (required)
[x] I have updated the changelog accordingly (required).
[ ] My change requires a change to the documentation.
[ ] I have updated the tests accordingly (required for a bug fix or a new feature).
[ ] I have updated the documentation accordingly.
[x] I have reformatted the code using make format (required)
[x] I have checked the codestyle using make check-codestyle and make lint (required)
[x] I have ensured make pytest and make type both pass. (required)

Note: we are using a maximum length of 127 characters per line