test(convert): cover never_convert_lossy_files in playlist entry tests

[Kidus5168]

Summary

Add a never_convert_lossy_files parametrize case to test_playlist_entry in the convert plugin tests.

This verifies that when never_convert_lossy_files=True prevents transcoding of a lossy file, the generated playlist entry correctly keeps the original file extension rather than replacing it with the target format extension.

Test plan

• poetry run pytest test/plugins/test_convert.py -k playlist -v — all 7 tests pass

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.80%. Comparing base (c90f42d) to head (c80612d).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6812      +/-   ##
==========================================
+ Coverage   74.78%   74.80%   +0.01%     
==========================================
  Files         163      163              
  Lines       20966    20966              
  Branches     3302     3302              
==========================================
+ Hits        15680    15684       +4     
+ Misses       4529     4527       -2     
+ Partials      757      755       -2     

see 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.