Update actions/cache action to v5 (#46)

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

Author: renovate[bot]

.github/workflows/docs.yaml

@@ -20,7 +20,7 @@ jobs:
           python-version: 3.x
       - 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