Adds dict conversion test for ActuatorBase configs

[mschweig]

Description

A recent PR (#1530 (comment)) causes issues with joint_parameter_lookup attributes of Articulation Configs. The class_to_dict utility function needs to return a primitive dict. Returning a torch.Tensor conflicts with OmegaConf.

This PR adds a unittest for the dict conversion as requested by @lgulich so that the issue can be fixed. The test case fails on main branch as expected according to my understanding. Passes on v1.3.0.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there