fix docs GH workflow

.github/workflows/docs-gh-pages.yml

@@ -5,6 +5,9 @@ on:
       - main
   # Run this workflow when a tag or branch is created
   create:
+
+  # trigger manually
+  workflow_dispatch:
 jobs:
   build:
     if: github.event_name == 'create' && github.event.ref_type == 'tag' && github.event.repository.fork == false
@@ -13,6 +16,10 @@ jobs:
       CONFIGDB_URL: http://configdb-dev
     steps:
     - uses: actions/checkout@v2
+    - name: Set up Python
+      uses: actions/setup-python@v4
+      with:
+        python-version: '3.9'
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip