Update actions/cache to v4

Author: fkettelhoit

.github/workflows/test.yml

@@ -12,7 +12,7 @@ jobs:
         with:
           toolchain: stable
       - name: Cache target
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         env:
           cache-name: cache-default-target-and-lockfile
         with: