Bump OS & Python for docs build

.readthedocs.yaml

@@ -1,8 +1,8 @@
 version: 2
 build:
-  os: ubuntu-20.04
+  os: ubuntu-22.04
   tools:
-    python: "3.9"
+    python: "3.12"
 mkdocs:
   configuration: mkdocs.yml
 python: