Type check before testing in GitHub workflow

Author: v--

.github/workflows/python-package.yml

@@ -30,7 +30,10 @@ jobs:
         python -m pip install --upgrade pip
         python -m pip install twine
         python -m pip install sphinx
+        python -m pip install mypy
         if [ -f dev-requirements.txt ]; then pip install -r dev-requirements.txt; fi
+    - name: Check types
+      run: mypy
     - name: Run Tests
       run: |
         python tests.py