configure poetry to not create its own virtual env

this workflow runs in its own container with its own python.
hopefully, this setting will resolve the preceeding (see earlier
commits) venv ambiguity. (and we'll just all use the container's
python environment).

.github/workflows/pypi-release.yml

@@ -18,8 +18,8 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        python -m venv env  # create a virtual environment so poetry finds an uses this one
         python -m pip install poetry
+        poetry config virtualenvs.create false  # tell poetry not to create a new virtual environment
         poetry self add "poetry-dynamic-versioning[plugin]"
     - name: Build package with poetry
       run: |