setup python version for plugin doc check

Author: kezhenxu94

.github/workflows/CI.yaml

@@ -61,6 +61,10 @@ jobs:
         uses: actions/checkout@v4
         with:
           submodules: true
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: 3.8
       - name: Check plugin doc
         run: |
           make env