make sure test env has matplotlib

Author: woodthom2

.github/workflows/test.yml

@@ -30,6 +30,8 @@ jobs:
           python-version: ${{ matrix.python }}
       - name: Install Tox
         run: pip install tox
+      - name: Install Matplotlib
+        run: pip install matplotlib
       - name: Setup Java
         uses: actions/setup-java@v3
         with: