Fix bugs in kettle_asset.xml to ensure compatibility with the latest MuJoCo versions.

[Josh00-Lu]

Description

Explanation

There's a missing <default> tag in kettle_asset.xml. This will bring errors in the latest version of MuJoCo (>3.16). The problem is mentioned in: https://github.com/Farama-Foundation/D4RL/issues/236#issue-2420593982.

No dependencies are required for this change.

Type of change

Please delete options that are not relevant.

• [x] 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 not work as expected)
• [ ] This change requires a documentation update

Screenshots

Please attach before and after screenshots of the change if applicable.

Checklist:

• [x] I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[Kallinteris-Andreas]

@Josh00-Lu can you make this PR in https://github.com/Farama-Foundation/Gymnasium-Robotics, and also validate that this change does not change the behavior of the environment for older versions of mujoco (3.1.6, 3.0.1, 2.3.7, 2.2.2, 2.1.5)

[Josh00-Lu]

@Josh00-Lu can you make this PR in https://github.com/Farama-Foundation/Gymnasium-Robotics, and also validate that this change does not change the behavior of the environment for older versions of mujoco (3.1.6, 3.0.1, 2.3.7, 2.2.2, 2.1.5)

Sure.

[Josh00-Lu]

I have submit a PR in https://github.com/Farama-Foundation/Gymnasium-Robotics/pull/255.