Hotfix PPO + gSDE

[araffin]

Description

closes #52
closes #54

Motivation and Context

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

Types of changes

• 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)

Checklist:

• I've read the CONTRIBUTION guide (required)
• 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.
• I have checked the codestyle using make lint
• I have ensured make pytest and make type both pass.

[araffin]

@Miffyli I will merge this one as soon as the tests pass because it is a hotfix (I will also do a release on pypi).