Bug: Update Codecov integration

[DeborahOlaboye]

🗒️ Description

Codecov updated its GitHub integration and now requires OIDC + Codecov App. See: https://about.codecov.io/blog/codecov-is-updating-its-github-integration/

Maintainer action: Please install the Codecov GitHub App on this repository or the ethereum organization to enable OIDC-based uploads.

This PR updates the GitHub Actions workflow to be compatible with the new Codecov integration and ensures that coverage reports are correctly uploaded and annotated on PRs.

🔗 Related Issues or PRs

N/A.

Fixes #1458

✅ Checklist

• All: Ran fast tox checks to avoid unnecessary CI fails, see also Code Standards and Enabling Pre-commit Checks:

  uvx tox -e static

• All: PR title adheres to the repo standard - it will be used as the squash commit message and should start type(scope):.
• All: Considered adding an entry to CHANGELOG.md.
• All: Considered updating the online docs in the ./docs/ directory.
• All: Set appropriate labels for the changes (only maintainers can apply labels).
• Tests: Ran mkdocs serve locally and verified the auto-generated docs for new tests in the Test Case Reference are correctly formatted.
• Tests: For PRs implementing a missed test case, update the post-mortem document to add an entry the list.
• Ported Tests: All converted JSON/YML tests from ethereum/tests or tests/static have been assigned @ported_from marker.

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