Add sphinx.configuration key to .readthedocs.yaml

See: https://about.readthedocs.com/blog/2024/12/deprecate-config-files-without-sphinx-or-mkdocs-config/

Author: axelf4

.readthedocs.yaml

@@ -9,6 +9,9 @@ build:
     pre_build:
       - scripts/evil-extract-docstrings
 
+sphinx:
+  configuration: doc/source/conf.py
+
 python:
   install:
     - requirements: doc/requirements.txt