chore: upgrade to latest readthedocs config format

.readthedocs.yml

@@ -3,11 +3,14 @@
 
 # Required
 version: 2
+build:
+  os: ubuntu-22.04
+  tools:
+    python: '3.7'
 
 # How to install the project.  We need to specify to use `pip`, because 
 # otherwise RTD may try to directly execute `setup.py`, which doesn't exist.
 python:
-  version: 3.7
   install:
     - method: pip
       path: .