CI: Codecov upload step can fail even when tests pass

[t-uda]

Summary

The CI workflow on main failed on March 25, 2026 after the v0.1.2 release merge, even though the test job itself passed.

• Failed run: https://github.com/t-uda/ellphi/actions/runs/23530274697
• Failing step: Upload coverage reports to Codecov in .github/workflows/python-app.yml
• Affected job: test (3.10)
• Test result in that job: 243 passed

Observed failure

The failure happened in codecov/codecov-action@v4.0.1, not in pytest:

• Could not pull latest version information: SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON\n- Error: write EPIPE\n\nThis means the workflow can report a red CI status on main even when the package itself is fine.\n\n## Follow-up\n- Decide whether Codecov upload should be non-blocking for branch protection purposes\n- Consider updating codecov/codecov-action to a newer version\n- Check whether any extra changes are needed for the upcoming Node.js 24 migration, since the same run also showed Node.js 20 deprecation annotations\n\n## Files\n- .github/workflows/python-app.yml\n

[t-uda]

Fixed in PR #132 (merged): codecov/codecov-action bumped v4.0.1 → v5 and the upload step is now non-blocking (continue-on-error: true), so a Codecov outage can no longer fail CI when tests pass.