Update actions/cache action to v5 (#68)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/build-website.yml

@@ -35,7 +35,7 @@ jobs:
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@v4
       - run: echo "CACHE_ID=$(date --utc '+%V')" >> $GITHUB_ENV
-      - uses: actions/cache@v4
+      - uses: actions/cache@v5
         with:
           key: mkdocs-material-${{ env.CACHE_ID }}
           path: .cache