🐛 Template: Fix MyST Github Pages action

The automatically generated Github Pages action to deploy the MyST documentation was
broken, because it assumes the content is in the root folder. Here we add the
`working_directory` for the HTML build step and correct the `path` for the upload step.

Author: mbercx

template/{% if doc_deploy == 'github' %}.github{% endif %}/workflows/{% if doc_deploy == 'github' and docs == 'myst' %}deploy-myst.yaml{% endif %}

@@ -36,10 +36,11 @@ jobs:
         run: npm install -g mystmd
       - name: Build HTML Assets
         run: myst build --html
+        working-directory: docs
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v3
         with:
-          path: './_build/html'
+          path: 'docs/_build/html'
       - name: Deploy to GitHub Pages
         id: deployment
         uses: actions/deploy-pages@v4