Add build information to readthedocs

.readthedocs.yml

@@ -1,13 +1,18 @@
 version: 2
 
+build:
+  os: ubuntu-22.04
+  tools:
+    python: 3.9
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/conf.py
 
 formats: all
 
 python:
-  version: 3.7
+  version: 3.9
   install:
     - requirements: requirements.txt
     - requirements: dev-requirements.txt