Only restore cache for playground.

Author: 01mf02

.github/workflows/playground.yml

@@ -25,7 +25,7 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v4
 
-    - uses: actions/cache@v4
+    - uses: actions/cache/restore@v4
       with:
         path: |
           ~/.cargo/registry/index/