ci: bump actions/cache to v4

Author: ValuedMammal

.github/workflows/cont_integration.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
       - name: Cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: |
             ~/.cargo/registry