fix: re-enable PHPUnit test step in tests.yml

Tests were commented out in PR #10. PHPUnit test files exist in
tests/phpunit/ and phpunit.xml is configured. Re-enabling the step
so tests actually run in CI.

Closes #45

.github/workflows/tests.yml

@@ -34,11 +34,8 @@ jobs:
       - name: Install dependencies
         run: composer install --prefer-dist --no-progress
 
-      # - name: Debug test file content
-      #   run: echo "--- Debugging tests/test-admin.php lines 75-95 ---" && sed -n '75,95p' tests/test-admin.php && echo "--- End Debugging ---"
-
-      # - name: Run tests
-      #   run: ./vendor/bin/phpunit
+      - name: Run tests
+        run: ./vendor/bin/phpunit
 
   code-style:
     name: Code Style