fix: update GATEWAY_URL environment variable to use vars

Author: Gioee

.github/workflows/test.yml

@@ -34,7 +34,7 @@ jobs:
         env:
           CHINOOK_DATABASE_URL: ${{ secrets.CHINOOK_DATABASE_URL }}
           CHINOOK_API_KEY: ${{ secrets.CHINOOK_API_KEY }}
-          GATEWAY_URL: ${{ secrets.GATEWAY_URL }}
+          GATEWAY_URL: ${{ vars.GATEWAY_URL }}
         run: npm test
       - name: Upload Code Coverage
         uses: codecov/codecov-action@v4