Update cache action to version 4

Author: Zahnentferner

.github/workflows/nextjs.yml

@@ -62,7 +62,7 @@ jobs:
           # You may remove this line if you want to manage the configuration yourself.
           static_site_generator: next
       - name: Restore cache
-        uses: actions/cache@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9 # v4.0.2
+        uses: actions/cache@v4
         with:
           path: |
             .next/cache