fix: Add install poetry step.

Author: mike-oakley

.github/workflows/test.yml

@@ -20,5 +20,11 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         python -m pip install tox tox-gh-actions
+    - name: Install Poetry
+      uses: snok/install-poetry@v1
+      with:
+        version: 1.5.0
+        virtualenvs-create: true
+        virtualenvs-in-project: true
     - name: Run tox test suite
       run: tox