Update readthedocs config

see https://docs.readthedocs.io/en/stable/config-file/v2.html#build-os
> The configuration key build.os is required to build your documentation.

.readthedocs.yml

@@ -12,9 +12,12 @@ sphinx:
 # Optionally build your docs in additional formats such as PDF and ePub
 formats: all
 
-# Optionally set the version of Python and requirements required to build your docs
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.11"
+
 python:
-  version: 3.7
   install:
     - requirements: requirements_docs.txt
     - method: pip