Add mypy dependency

Author: dixonjoel

.github/workflows/test_actions.yml

@@ -277,6 +277,8 @@ jobs:
         run: cat test-project/pyproject.toml
       - name: Add ni-python-styleguide to the project
         run: poetry add ni-python-styleguide -C test-project
+      - name: Add mypy to the project
+        run: poetry add mypy -C test-project
       - name: Create poetry.lock
         run: poetry lock -C test-project
       - name: Check that the project was created