Fixes viewport controller import (#219)

# Description

This PR fixes an outdated import in viewport camera controller

## Type of change

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applicable. -->

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

## Checklist

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

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source/isaaclab/isaaclab/envs/ui/viewport_camera_controller.py

@@ -14,7 +14,8 @@ from typing import TYPE_CHECKING
 
 import omni.kit.app
 import omni.timeline
-from omni.isaac.lab.assets.articulation.articulation import Articulation
+
+from isaaclab.assets.articulation.articulation import Articulation
 
 if TYPE_CHECKING:
     from isaaclab.envs import DirectRLEnv, ManagerBasedEnv, ViewerCfg