ci(tests): Check mypy

See also: http://mypy-lang.org/

Author: tony

.github/workflows/tests.yml

@@ -62,6 +62,9 @@ jobs:
       - name: Lint with flake8
         run: poetry run flake8
 
+      - name: Lint with mypy
+        run: poetry run mypy .
+
       - name: Test with pytest
         run: poetry run py.test --cov=./ --cov-report=xml