Fixes docstring for semantic_segmentation_mapping (#367)

# Description

Fixes docstring description of dictionary example for CameraCfg
semantic_segmentation_mapping to properly format dictionary in
documentation.

Fixes # (issue)

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## Type of change

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- This change requires a documentation update


## 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/sensors/camera/camera_cfg.py

@@ -119,7 +119,9 @@ class CameraCfg(SensorBaseCfg):
     """Dictionary mapping semantics to specific colours
 
     Eg.
-    ```
+
+    .. code-block:: python
+
         {
             "class:cube_1": (255, 36, 66, 255),
             "class:cube_2": (255, 184, 48, 255),
@@ -128,5 +130,5 @@ class CameraCfg(SensorBaseCfg):
             "class:ground": (100, 100, 100, 255),
             "class:robot": (61, 178, 255, 255),
         }
-    ```
+
     """