Add a testcase for ts compile -> saving with torch_tensorrt.save

[narendasan]

Description

Adds a testcase to cover #3775

Type of change

Please delete options that are not relevant and/or add your own.

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] My code follows the style guidelines of this project (You can use the linters)
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas and hacks
• [x] I have made corresponding changes to the documentation
• [x] I have added tests to verify my fix or my feature
• [x] New and existing unit tests pass locally with my changes
• [x] I have added the relevant labels to my PR in so that relevant reviewers are notified