Add sphinx.configuration to .readthedocs.yml (#2740) (#2771)

(cherry picked from commit 1f66af5)

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

Author: github-actions[bot]

.readthedocs.yml

@@ -14,3 +14,6 @@ python:
     - path: .
       extra_requirements:
         - "docs"
+
+sphinx:
+  configuration: docs/sphinx/conf.py