ci: bump actions/setup-node from 4 to 6 (#26)

Author: dependabot[bot]

.github/workflows/copilot-setup-steps.yml

@@ -20,7 +20,7 @@ jobs:
         uses: actions/checkout@v6
 
       - name: Set up Node.js
-        uses: actions/setup-node@v4
+        uses: actions/setup-node@v6
         with:
           node-version: "20"
           cache: "npm"