upgrade actions for docs build

.github/workflows/docs.yml

@@ -6,9 +6,9 @@ jobs:
       runs-on: ubuntu-latest
       steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Set up Python 3.8
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@v5
         with:
           python-version: 3.8
       - name: install sphinx