Run GitHub actions publish job after successful test and docs job

.github/workflows/ci.yml

@@ -46,3 +46,28 @@ jobs:
         run: pip install tox
       - name: Check docs
         run: tox -e docs
+
+  publish:
+    needs: [test, docs]  # only run if previous jobs are successful
+    runs-on: ubuntu-18.04
+    steps:
+    - uses: actions/checkout@master
+    - name: Set up Python 3.7
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.7
+    - name: Install pypa/build
+      run: python -m pip install build --user
+    - name: Build a source tarball
+      run: python -m build --sdist --outdir dist/ .
+    - name: Publish package to Test PyPI
+      uses: pypa/gh-action-pypi-publish@master
+      with:
+        password: ${{ secrets.TEST_PYPI_API_TOKEN }}
+        repository_url: https://test.pypi.org/legacy/
+        skip_existing: true
+    - name: Publish package to PyPI
+      if: startsWith(github.ref, 'refs/tags')
+      uses: pypa/gh-action-pypi-publish@master
+      with:
+        password: ${{ secrets.PYPI_API_TOKEN }}