Without this fix I get the following error when enabling the action plot
in the IsaacSim GUI:

```
2025-01-28 08:28:06 [594,911ms] [Error] [omni.ui.python] NameError: name 'isaacsim' is not defined

At:
  IsaacLab/source/isaaclab/isaaclab/ui/widgets/line_plot.py(501): _build_filter_frame
  IsaacLab/source/isaaclab/isaaclab/sim/simulation_context.py(508): render
  IsaacLab/source/isaaclab/isaaclab/envs/manager_based_rl_env.py(193): step
  venv/lib/python3.10/site-packages/gymnasium/core.py(322): step
  venv/lib/python3.10/site-packages/gymnasium/wrappers/common.py(393): step
  IsaacLab/scripts/environments/inference_agent.py(104): main
  IsaacLab/scripts/environments/inference_agent.py(110): <module>
```

- Bug fix (non-breaking change which fixes an issue)

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] 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
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there