Fix the cache for docs ci (#25)

Author: wu-clan

.github/workflows/docs.yml

@@ -19,7 +19,7 @@ jobs:
         with:
           python-version: 3.x
       - run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV
-      - uses: actions/cache@v4FUNDING.yml
+      - uses: actions/cache@v4
         with:
           key: mkdocs-material-${{ env.cache_id }}
           path: .cache