relax codecov workflow requirement and condition.

[fujitatomoya]

Description

address GitHub Actions secrets-on-fork-PRs problem for codecov.

Fixes # (issue)

Is this user-facing behavior change?

No

Did you use Generative AI?

Yes, partially with Claude Opus 4.8 but this is actually permission control.

Additional Information

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.26%. Comparing base (6b64c4a) to head (7416838).

Additional details and impacted files

@@           Coverage Diff            @@
##           rolling     #390   +/-   ##
========================================
  Coverage    88.26%   88.26%           
========================================
  Files           24       24           
  Lines          622      622           
  Branches        65       65           
========================================
  Hits           549      549           
  Misses          53       53           
  Partials        20       20           

Flag	Coverage Δ
unittests	88.26% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.