Fix: update file path in eagle3 scripts (#654)

## What does this PR do?

**Type of change:** Bug fix <!-- Use one of the following: Bug fix, new
feature, new example, new tests, documentation. -->

**Overview:** 
Update file path

## Usage
<!-- You can potentially add a usage example below. -->

```python
# Add a code snippet demonstrating how to use this
```

## Testing
<!-- Mention how have you tested your change if applicable. -->

## Before your PR is "*Ready for review*"
<!-- If you haven't finished some of the above items you can still open
`Draft` PR. -->

- **Make sure you read and follow [Contributor
guidelines](https://github.com/NVIDIA/TensorRT-Model-Optimizer/blob/main/CONTRIBUTING.md)**
and your commits are signed.
- **Is this change backward compatible?**: Yes/No <!--- If No, explain
why. -->
- **Did you write any new necessary tests?**: Yes/No
- **Did you add or update any necessary documentation?**: Yes/No
- **Did you update
[Changelog](https://github.com/NVIDIA/TensorRT-Model-Optimizer/blob/main/CHANGELOG.rst)?**:
Yes/No <!--- Only for new features, API changes, critical bug fixes or
bw breaking changes. -->

## Additional Information
<!-- E.g. related issue. -->

Signed-off-by: h-guo18 <[email protected]>

Author: h-guo18

examples/speculative_decoding/train_eagle3_and_export.sh

@@ -78,9 +78,9 @@ mkdir -p "$(dirname "$OUTPUT_DIR")"
             --eagle_config eagle_config.json
 
 echo "==== [2/3] Evaluating ModelOpt checkpoint on MT-Bench ===="
-python ar_validate.py --model_path $OUTPUT_DIR
+python scripts/ar_validate.py --model_path $OUTPUT_DIR
 
 echo "==== [3/3] Exporting checkpoint to deployment format ===="
 EXPORT_PATH=export/${MODEL_BASENAME}-$(date +%Y%m%d_%H%M)
 mkdir -p "$(dirname "$EXPORT_PATH")"
-python export_hf_checkpoint.py --model_path $OUTPUT_DIR --export_path $EXPORT_PATH
+python scripts/export_hf_checkpoint.py --model_path $OUTPUT_DIR --export_path $EXPORT_PATH