Update .readthedocs.yml

readthedocs/readthedocs.org#4912 (comment)

.readthedocs.yml

@@ -22,8 +22,8 @@ build:
         post_install:
             # Install dependencies with 'docs' dependency group
             # https://python-poetry.org/docs/managing-dependencies/#dependency-groups
-            - poetry install --with docs
-            - poetry shell
+            - VIRTUAL_ENV=$READTHEDOCS_VIRTUALENV_PATH poetry install --with docs
+
 # Build documentation in the "docs/" directory with Sphinx
 sphinx:
     configuration: docs/conf.py