ci: add codecov secret

Author: bruno-fs

.github/workflows/tests.yml

@@ -156,4 +156,6 @@ jobs:
           nox --session=coverage -- xml
 
       - name: Upload coverage report
-        uses: codecov/codecov-action@v4.5.0
+        uses: codecov/codecov-action@v5.4.0
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}