ci(workflows): skip Unity tests for forked repository PRs

Add conditional check to skip Unity tests when running workflows
from forked repositories, where secrets are not available. This
allows external contributors to still get CI feedback on build
and unit tests while gracefully handling missing Unity credentials.

The workflow will run Unity tests for:
- PRs from branches in the main repository
- Any case where Unity secrets are available

Co-Authored-By: Claude <noreply@anthropic.com>

Author: JasonXuDeveloper

.github/workflows/ci.yml

@@ -84,6 +84,8 @@ jobs:
             Library-
 
       - name: Run Unity tests
+        # Skip Unity tests for external PRs (secrets not available in forks)
+        if: github.event.pull_request.head.repo.full_name == github.repository || secrets.UNITY_EMAIL != ''
         uses: game-ci/unity-test-runner@v4
         id: unity-tests
         env: