test(package_list_parser): Improve test coverage for package_list

[JigyasuRajput]

Description:

FIxes #4875

This PR enhances the test coverage for package_list_parser.py by adding unit tests for its core functions.

Changes:

• Added tests for parse_list, add_vendor, parse_data, and check_file functions.
• Included various package manager scenarios (dpkg, rpm, pacman, pip).
• Added edge case tests for handling missing/malformed data.
• Improved assertions to ensure correctness of parsed package lists.

Why this is needed:

• Improves test coverage and ensures correctness.
• Catches potential issues with different package manager formats.

Testing:

All test cases passed.

[JigyasuRajput]

Hey!
I think the gitlint can be fixed, but the another test failure usually happens when the network isn’t reachable or the connection isn’t properly routed. Maybe re-running CI would fix it? (but I'm not sure for this one)