Merge pull request zxcalc#202 from dlyongemallo/fix_tests_mypy

Enforce mypy on tests on presubmit.

.github/workflows/pythonpackage.yml

@@ -29,7 +29,7 @@ jobs:
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
     - name: mypy
       run: |
-        mypy pyzx/
+        mypy pyzx/ tests/
     - name: Test with unittest
       run: |
         python -m unittest discover -s "tests" -t "."