Publish to PyPI manually, not via marketplace.

Previously we were using a GitHub Marketplace action for this, but
this turns out not to be quite flexible enough for what we're trying to do here.

.github/workflows/publish.yaml

@@ -18,14 +18,21 @@ jobs:
         with:
           python-version: "3.9"
 
+      - name: Install Poetry >= 1.2.0a
+        run: |
+          curl -sSL https://raw.githubusercontent.com/python-poetry/poetry/master/install-poetry.py -O &&
+          python install-poetry.py --preview
+
+      - name: Install dependencies
+        run: poetry install
+
+      - name: Install poetry-version-plugin
+        run: poetry plugin add poetry-version-plugin
+
       - name: Build and publish to pypi
-        uses: JRubics/poetry-publish@v1  # https://github.com/marketplace/actions/publish-python-poetry-package
-        with:
-          python_version: '3.9.0'
-          poetry_version: '>=1.2.0a1'
-          pypi_token: ${{ secrets.PYPI_TOKEN }}
-          repository_name: 'blackbox-cli'
-          repository_url: 'https://pypi.org/project/blackbox-cli/'
+        run: |
+          poetry config pypi-token.pypi ${{ secrets.PYPI_TOKEN }} &&
+          poetry publish --build
 
   build-and-push-on-release:
     name: Build and push