test(output_engine): add regression tests for unset data

[JigyasuRajput]

Description:

Fixes #4441 this PR introduces regression tests to verify OutputEngine behavior when certain optional fields are unset. Specifically, it addresses cases like sbom_serial_number to prevent future issues similar to #4438.

Changes Made:

• Added a test case test_output_with_unset_fields in test_output_engine.py
• Ensures OutputEngine initializes correctly when sbom_serial_number is missing
• Uses subTest to allow future extension for more unset fields
• Verifies that output_cves does not raise exceptions when handling missing values

Testing:

• Verified output consistency when sbom_serial_number is unset

[terriko]

This looks ok. I'm going to let the tests run and come back for a more careful review once they're passing. Thank you!

[terriko]

Merge time! Thank you again, I'm very glad to have a regression test here.