upgrade actions/cache@v4

Author: foxzool

.github/workflows/ci.yaml

@@ -48,7 +48,7 @@ jobs:
       - name: Checkout sources
         uses: actions/checkout@v2
       - name: Cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: |
             ~/.cargo/bin/