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)

[terriko]

I think this is ok to merge, but I'm going to go ahead and update the branch for safety since it's pretty old. I'll set it to merge if the tests pass.