Add missing sphinx.configuration RtD setting (#225) (#226)

(cherry picked from commit a34673a)

Co-authored-by: Quentin Pradet <[email protected]>

Author: github-actions[bot]

.readthedocs.yml

@@ -17,4 +17,5 @@ python:
         - develop
 
 sphinx:
+  configuration: docs/sphinx/conf.py
   fail_on_warning: true