Update actions/cache action to v6 (#19)

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

Author: renovate[bot]

.github/workflows/hugo.yaml

@@ -65,7 +65,7 @@ jobs:
       - name: Install Node.js dependencies
         run: npm ci
 
-      - uses: actions/cache@v4
+      - uses: actions/cache@v6
         with:
           path: ${{ env.HUGO_CACHEDIR }}
           key: ${{ runner.os }}-hugo-${{ hashFiles('**/go.sum') }}