CI: Add a pull request workflow

Runs tox pep8 and releasenotes environments.

Author: markgoddard

.github/workflows/pull-request.yml

@@ -0,0 +1,28 @@
+---
+name: Pull request
+'on':
+  pull_request:
+jobs:
+  tox:
+      runs-on: ubuntu-20.04
+      strategy:
+        matrix:
+          include:
+            - environment: pep8
+              python-version: 3.6 
+            - environment: releasenotes
+              python-version: 3.6 
+      name: Tox ${{ matrix.environment }} with Python ${{ matrix.python-version }}
+      steps:
+        - name: Github Checkout 🛎u
+          uses: actions/checkout@v3
+          with:
+            fetch-depth: 0
+        - name: Setup Python ${{ matrix.python-version }} 🐍
+          uses: actions/setup-python@v3
+          with:
+            python-version: ${{ matrix.python-version }}
+        - name: Install Tox 📦
+          run: pip install tox 
+        - name: Run Tox ${{ matrix.environment }} 🧪
+          run: tox -e ${{ matrix.environment }}