update GitHub Actions workflow to use pnpm for dependency installation and build

Author: py-dev-nandini-12

.github/workflow/deploy.yml

@@ -19,10 +19,10 @@ jobs:
           node-version: 18
 
       - name: Install dependencies
-        run: npm install
+        run: pnpm install
 
       - name: Build Next.js app
-        run: npm run build
+        run: pnpm run build
 
       - name: Deploy to Vercel
         run: npx vercel --token=${{ secrets.VERCEL_TOKEN }} --prod