Wrong file name in error message for invalid initialization_script in NotebookJobStep

[fakio]

Describe the bug
If you use an initialization_script that doesn't exist in NotebookJobStep you receive an error message that informs the input notebook name instead of the initialization_script name.

The error seems at https://github.com/aws/sagemaker-python-sdk/blob/master/src/sagemaker/workflow/notebook_job_step.py#L267

To reproduce

steps = [NotebookJobStep(
    image_uri="885854791233.dkr.ecr.us-east-1.amazonaws.com/sagemaker-distribution-prod:1-cpu",
    kernel_name="python3",
    input_notebook="job-test/job.ipynb",
    initialization_script="invalid-file.sh",
)]
pipeline = Pipeline(
    name="pipeline",
    steps=steps,
)
pipeline.upsert(role_arn=role)

Expected behavior
ValueError: Validation Errors:

• The initialization script(invalid-file.sh) is not a valid file.

Screenshots or logs
ValueError: Validation Errors:

• The initialization script(job-test/job.ipynb) is not a valid file.