Fixes import order in multi_asset.py (#536)

# Description

Fixes bug introduced in the import order of multi_asset.py where isaac
sim import was happening before launching the AppLauncher.

## 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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scripts/demos/multi_asset.py

@@ -19,8 +19,6 @@ from __future__ import annotations
 
 import argparse
 
-from isaacsim.core.utils.stage import get_current_stage
-
 from isaaclab.app import AppLauncher
 
 # add argparse arguments
@@ -39,6 +37,7 @@ simulation_app = app_launcher.app
 
 import random
 
+from isaacsim.core.utils.stage import get_current_stage
 from pxr import Gf, Sdf
 
 import isaaclab.sim as sim_utils