Fix test workflow failure by granting push permissions to GITHUB_TOKEN

[Copilot]

The test GitHub Actions job was failing after successful pytest execution because the workflow could not push the README update (403 Write access to repository not granted). This PR addresses the permission gap in the workflow token scope.

• Workflow permission fix

  • Added explicit workflow-level permissions to allow the existing Commit and push README step to push changes.
  • No behavior changes to test execution, artifact upload, or README generation logic.

• Scope

  • Single-file, surgical change in .github/workflows/tests.yml.
  • Leaves current commit/push mechanism intact; only enables required auth scope.

permissions:
  contents: write