fixes to readthedocs build process

.readthedocs.yaml

@@ -3,9 +3,10 @@
  build:
    os: "ubuntu-24.04"
    tools:
-     python: "3.12"
+     python: "3.13"
    jobs:
      pre_install:
+       - pip install --upgrade pip
        - pip install --group docs
 
  mkdocs: