Attempt to fix doc build

.readthedocs.yaml

@@ -5,6 +5,12 @@
 # Required
 version: 2
 
+# Set the version of Python and other tools you might need
+build:
+   os: ubuntu-22.04
+   tools:
+      python: "3.8"
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
    configuration: docs/conf.py
@@ -13,8 +19,7 @@ sphinx:
 formats:
    - pdf
 
-# Optionally set the version of Python and requirements required to build your docs
+# We recommend specifying your dependencies to enable reproducible builds:
 python:
-   version: 3.8
    install:
    - requirements: docs/requirements.txt