Update rtd build environment etc

.readthedocs.yaml

@@ -1,29 +1,17 @@
 # Configuration on how ReadTheDocs (RTD) builds our documentation
 # ref: https://readthedocs.org/projects/native-authenticator/
 # ref: https://docs.readthedocs.io/en/stable/config-file/v2.html
-
-# Required (RTD configuration version)
+#
 version: 2
 
-# Set the version of Python and other tools you might need
 build:
-  os: ubuntu-20.04
+  os: ubuntu-lts-latest
   tools:
-    python: "3.9"
+    python: "3.12"
 
-# Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/source/conf.py
 
-# Optionally build your docs in additional formats such as PDF and ePub
-formats: []
-
 python:
   install:
-    # WARNING: This requirements file will be installed without the pip
-    #          --upgrade flag in an existing environment. This means that if a
-    #          package is specified without a lower boundary, we may end up
-    #          accepting the existing version.
-    #
-    #          ref: https://github.com/readthedocs/readthedocs.org/blob/0e3df509e7810e46603be47d268273c596e68455/readthedocs/doc_builder/python_environments.py#L335-L344
     - requirements: docs/requirements.txt