Update gh-pages.yml (#300)

.github/workflows/gh-pages.yml

@@ -14,6 +14,8 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4
+        with:
+            python-version: '3.9'
 
       - name: Install dependencies
         run: pip install -r docs/requirements.txt
@@ -44,4 +46,4 @@ jobs:
         with:
           folder: _build
           clean-exclude: |
-            *.*.*/
+            *.*.*/