doc: readthedocs build settings

.readthedocs.yml

@@ -5,6 +5,12 @@
 # Required
 version: 2
 
+# Set the version of Python and other tools you might need
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.9"
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/source/conf.py
@@ -19,6 +25,5 @@ sphinx:
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.8
   install:
     - requirements: docs/source/requirements.txt