[EngSys] remove npm cache from copilot setup

as currently we are using pnpm via rush.

Author: jeremymeng

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

@@ -26,7 +26,6 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: "22"
-          cache: "npm"
 
       - name: Install Rush
         run: npm install -g @microsoft/rush