plugins: move doc build to python 3.11

Author: Morg42

.github/workflows/builddevdoc.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [ '3.9' ]
+        python-version: [ '3.11' ]
     name: Python ${{ matrix.python-version }}
     steps:
       - name: update OS (Ubuntu)