Add missing package for publishing

After separating build and publish step, the publish job didn't have `poetry` installed.

.github/workflows/build.yml

@@ -41,5 +41,7 @@ jobs:
         with:
           name: build
           path: dist
+      - name: install Poetry
+        uses: abatilo/[email protected]          
       - name: upload wheel and source
         run: poetry publish --username __token__ --password ${{ secrets.PYPI_TOKEN }}