Fixes deprecation warning for pxr.Semantics (#2721)

# Description

pxr.Semantics was deprecated in Isaac Sim 4.2 and is now Semantics. This
PR replaces imports of pxr.Semantics with Semantics if available.

## 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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Author: kellyguo11

source/isaaclab/isaaclab/sim/spawners/from_files/from_files.py

@@ -11,7 +11,13 @@
 import isaacsim.core.utils.stage as stage_utils
 import omni.kit.commands
 import omni.log
-from pxr import Gf, Sdf, Semantics, Usd
+from pxr import Gf, Sdf, Usd
+
+# from Isaac Sim 4.2 onwards, pxr.Semantics is deprecated
+try:
+    import Semantics
+except ModuleNotFoundError:
+    from pxr import Semantics
 
 from isaaclab.sim import converters, schemas
 from isaaclab.sim.utils import bind_physics_material, bind_visual_material, clone, select_usd_variants

source/isaaclab/test/sensors/test_tiled_camera.py

@@ -25,7 +25,13 @@
 import omni.replicator.core as rep
 import pytest
 from isaacsim.core.prims import SingleGeometryPrim, SingleRigidPrim
-from pxr import Gf, Semantics, UsdGeom
+from pxr import Gf, UsdGeom
+
+# from Isaac Sim 4.2 onwards, pxr.Semantics is deprecated
+try:
+    import Semantics
+except ModuleNotFoundError:
+    from pxr import Semantics
 
 import isaaclab.sim as sim_utils
 from isaaclab.sensors.camera import Camera, CameraCfg, TiledCamera, TiledCameraCfg