`env_vars` input has no visible effect on Codecov UI

According to the README, the env_vars input is described as:

Environment variables to tag the upload with (e.g. PYTHON | OS,PYTHON)

However, after uploading coverage reports with env_vars set, I can’t find these variables reflected anywhere on the Codecov UI. It seems like setting env_vars has no effect.

Here is an example coverage report where I configured env_vars:
🔗 https://app.codecov.io/github/vivodi/Flexget/commit/ff609bf951cbd68f710a02de2f9dab299f0674fe

- name: Upload coverage to Codecov
  uses: codecov/codecov-action@ad3126e916f78f00edff4ed0317cf185271ccc2d  # v5
  with:
    env_vars: OS,PYTHON
    fail_ci_if_error: true
    token: ${{ secrets.CODECOV_TOKEN }}

You can find the full GitHub Actions workflow here:
https://github.com/vivodi/Flexget/actions/runs/15089429373/workflow?pr=13

Could you tell me what the purpose of setting env_vars is?

Start with the README description of the env_vars input and the provided GitHub Actions workflow, then compare the configured upload with the linked Codecov report. Determine whether the variables should appear in the Codecov UI and document or correct the behavior so the purpose and expected result are clear.