Bump actions/cache from 3 to 4

Bumps [actions/cache](https://github.com/actions/cache) from 3 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v3...v4)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/docker-image.yml

@@ -34,7 +34,7 @@ jobs:
         run: docker save horaynarea/unbound_docker -o /images/unbound.tar.gz
 
       - name: Cache image
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /images/unbound.tar.gz
           key: ${{ github.run_id }}-${{ github.run_number }}-unbound
@@ -52,7 +52,7 @@ jobs:
           sudo chmod 777 /images
 
       - name: Load unbound cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /images/unbound.tar.gz
           key: ${{ github.run_id }}-${{ github.run_number }}-unbound