Migrate to UV: Activate venv for quarto

https://stackoverflow.com/questions/74668349/how-to-activate-a-virtualenv-in-a-github-action

Author: micedre

.github/workflows/publish-slides.yaml

@@ -32,7 +32,7 @@ jobs:
         run: uv run python -m nltk.downloader stopwords
 
       - name: Activate venv
-        run: source .venv/bin/activate
+        run: echo PATH=${GITHUB_WORKSPACE}/.venv/bin:$PATH >> $GITHUB_ENV
 
       - name: Publish to GitHub Pages (and render)
         uses: quarto-dev/quarto-actions/publish@v2