fix: upload coverage files only for latest stable version on release workflow

[dipinknair]

Release workflow runs the remote tests on 3 images which uploads coverage files with same name and causes below issue https://github.com/ansys/pymechanical/actions/runs/9209141487/job/25333060420

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.17%. Comparing base (7b0b1da) to head (666280a).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #748 +/- ## ======================================= Coverage 81.17% 81.17% ======================================= Files 32 32 Lines 2013 2013 ======================================= Hits 1634 1634 Misses 379 379 ```