Update Read the Docs config to fix build

Author: hugovk

.readthedocs.yml

@@ -1,11 +1,19 @@
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+# Project page: https://readthedocs.org/projects/installer/
+
 version: 2
 
 sphinx:
   builder: htmldir
   configuration: docs/conf.py
 
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3"
+
 python:
-  version: 3.8
   install:
     - requirements: docs/requirements.txt
     - method: pip