Merge PR #111 into unstable/v1

This patch adds a simple GHA-based smoke test that uses devpi to
verify the main success path of the action.

.github/workflows/test-upload.yml

@@ -0,0 +1,45 @@
+name: Test Upload
+
+on:
+  pull_request:
+  push:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    services:
+      devpi:
+        image: muccg/devpi
+        env:
+          DEVPI_PASSWORD: abcd1234
+        ports:
+          - 3141
+    steps:
+      - run: python3 -m pip install --upgrade pip build twine
+      - run: mkdir -p src/test_package
+      - run: echo '__version__ = "0.1"' > src/test_package/__init__.py
+      - run: echo "# Test Package" > README.md
+      - run: echo "$CONTENTS" > pyproject.toml
+        env:
+          CONTENTS: |
+            [build-system]
+            requires = ["setuptools>=61", "wheel"]
+            build-backend = "setuptools.build_meta"
+            [project]
+            name = "test-package"
+            version = "0.1"
+            readme = "README.md"
+      - run: python3 -m build
+      - run: twine register dist/*.tar.gz
+        env:
+          TWINE_USERNAME: root
+          TWINE_PASSWORD: abcd1234
+          TWINE_REPOSITORY_URL: http://localhost:${{ job.services.devpi.ports['3141'] }}/root/public/
+      - uses: actions/checkout@v3
+        with:
+          path: test
+      - uses: ./test
+        with:
+          user: root
+          password: abcd1234
+          repository_url: http://devpi:3141/root/public/