Add a GitHub workflow for pushing to PyPI and Test PyPI

In this commit I'm adding a new workflow which will build distributable
packages for pytest-localserver and upload them to PyPI and Test PyPI.
The uploads are treated as deployments, so they will not run until
someone manually approves them.

A future enhancement I'd like to make is to actually run tests using
the same package that is going to be uploaded. That's going to involve
tweaking tox to install from a prebuilt package rather than directly
from the source code, so it will take some time to figure that out.

Author: diazona

.github/workflows/release.yml

@@ -0,0 +1,59 @@
+name: Publish package to PyPI
+
+on:
+  release:
+    types:
+    - published
+
+jobs:
+  build:
+    name: Build distribution packages
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - name: Set up Python 3.10
+      uses: actions/setup-python@v4
+      with:
+        python-version: "3.10"
+    - name: Install pypa/build
+      run: |
+        python -m pip install --user build
+    - name: Build packages
+      run: |
+        pyproject-build
+    - uses: actions/upload-artifact@v3
+      with:
+        name: dist
+        path: dist/
+        if-no-files-found: error
+  publish-to-test-pypi:
+    name: Publish packages to Test PyPI
+    runs-on: ubuntu-latest
+    needs: [build]
+    environment: test-pypi
+    steps:
+    - uses: actions/download-artifact@v3
+      with:
+        name: dist
+        path: dist/
+    - name: Publish packages to Test PyPI
+      uses: pypa/gh-action-pypi-publish@release/v1
+      with:
+        password: '${{ secrets.TEST_PYPI_API_TOKEN }}'
+        repository_url: https://test.pypi.org/legacy/
+        print_hash: true
+  publish-to-pypi:
+    name: Publish packages to PyPI
+    runs-on: ubuntu-latest
+    needs: [build]
+    environment: pypi
+    steps:
+    - uses: actions/download-artifact@v3
+      with:
+        name: dist
+        path: dist/
+    - name: Publish packages to PyPI
+      uses: pypa/gh-action-pypi-publish@release/v1
+      with:
+        password: '${{ secrets.PYPI_API_TOKEN }}'
+        print_hash: true