add npm cache to action

src/Umbraco.Web.UI.Client/.github/workflows/playwright.yml

@@ -13,6 +13,7 @@ jobs:
     - uses: actions/setup-node@v2
       with:
         node-version: '16.x'
+        cache: 'npm'
     - name: Install dependencies
       run: npm ci
     - name: Install Playwright Browsers