ModelBuilder.register does not generate a repack step with a pipeline session in V3 but does in V2

**PySDK Version**
- [ ] PySDK V2 (2.x)
- [ X] PySDK V3 (3.x)

**Describe the bug**
ModelBuilder.register does not generate a repack step with a pipeline session in V3 but does in V2

**To reproduce**
A clear, step-by-step set of instructions to reproduce the bug.
The provided code need to be **complete** and **runnable**, if additional data is needed, please include them in the issue.

```
model_builder = ModelBuilder(
image_uri=image_uri,
s3_model_data_url=data_url,
source_code=SourceCode(
entry_script="infer.py",
source_dir=s3_script_archive,
),
role_arn=role,
sagemaker_session=pipeline_session,
env_vars={"SAGEMAKER_DEFAULT_INVOCATIONS_ACCEPT": "application/json"},
)
...
step_register = ModelStep(
name="RegisterModel",
step_args=model_builder.register(
content_types=["application/jsonlines"],
response_types=["application/json"],
inference_instances=[inference_instance_type],
transform_instances=[inference_instance_type],
model_package_group_name=model_package_group_name,
approval_status="Approved",
)
)
```

**Expected behavior**
A clear and concise description of what you expected to happen.
In V2, the model was repacked with the code present. In V3, the model is not, leaving the model unable to be repacked

**Screenshots or logs**
If applicable, add screenshots or logs to help explain your problem.

**System information**
A description of your system. Please provide:
- **SageMaker Python SDK version**: 2
- **Framework name (eg. PyTorch) or algorithm (eg. KMeans)**: ScikitLearn
- **Framework version**: 1.4.2
- **Python version**: 3.11
- **CPU or GPU**: CPU
- **Custom Docker image (Y/N)**: N

**Additional context**
Add any other context about the problem here.

pipeline_session で使用されるエントリーポイント ModelBuilder.register から開始し、その V3 の動作を、issue に記載されている V2 の動作と比較します。示されている SourceCode とモデルデータを使って ModelStep の登録を再現し、その後、repack ステップが生成され、登録されたモデルにコードが含まれていることを確認します。

索引モデルが issue の本文から書いたものです。