fix: update a deprecated config key so tests can run properly again

.readthedocs.yml

@@ -4,13 +4,16 @@
 
 # Required
 version: 2
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.8"
 
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/source/conf.py
   fail_on_warning: true
 
 python:
-  version: 3.8
   install:
     - requirements: requirements/doc.txt