fix(rtd): build with Python 3.11 so we can get Sphinx 8

Author: ntamas

.readthedocs.yaml

@@ -21,7 +21,7 @@ build:
     - zlib1g-dev
 
   tools:
-    python: "3.9"
+    python: "3.11"
     # You can also specify other tool versions:
     # nodejs: "16"
     # rust: "1.55"