Add missed test-threads=1 to coverage CI

[YJDoc2]

In #2685 I missed adding the test threads option to the coverage CI, due to which it still occasionally times out and fails. This adds that.

Also added in feature test script for uniformity, even though those are not failing

[codecov-commenter]

Codecov Report

Merging #2699 (9097a56) into main (0c068b8) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2699   +/-   ##
=======================================
  Coverage   65.40%   65.40%           
=======================================
  Files         133      133           
  Lines       16942    16942           
=======================================
  Hits        11081    11081           
  Misses       5861     5861           

[YJDoc2]

@containers/youki-maintainers going ahead and merging this as

1. the test-threads = 1 concept is already reviewed and approved in other PR
2. This only changes CI file and a script, both are validated by passing their corresponding CI