Update readthedocs config to install docs optional dependencies.

.readthedocs.yaml

@@ -8,13 +8,19 @@ version: 2
 # Set the OS, Python version and other tools you might need
 build:
   os: ubuntu-22.04
-  tools:
-    python: "3.12"
+  # tools:
+    # python: "3.12"
     # You can also specify other tool versions:
     # nodejs: "19"
     # rust: "1.64"
     # golang: "1.19"
 
+python:
+  version: 3.12
+  pip_install: true
+  extra_requirements:
+      - docs
+
 # Build documentation in the "docs/" directory with Sphinx
 sphinx:
   configuration: docs/conf.py