build(docs): fix Poetry install command

.readthedocs.yaml

@@ -10,7 +10,7 @@ build:
       - pip install poetry
       - poetry config virtualenvs.create false
     post_install:
-      - poetry install --only main docs --all-extras
+      - poetry install --only main,docs --all-extras
 
 # Build from the docs/ directory with Sphinx
 sphinx: