Bump README example to actions/setup-node@v6 to match repo workflows

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: sgoedecke

README.md

@@ -247,7 +247,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
 
       - name: Install Copilot CLI
         run: npm install -g @github/copilot