change back ci variable

.github/workflows/ci.yaml

@@ -32,7 +32,7 @@ jobs:
         with:
           os: "ubuntu-latest"
           python-version: "3.9"
-          venv-id: "docs-${{ runner.os }}"
+          venv-id: "docs"
           poetry-dependency-install-flags: "--all-extras --only 'main,docs'"
       - name: docs
         run: poetry run sphinx-build -W --keep-going -T -b html docs/source docs/build