Run mypy as part of GitHub workflows

Author: vlaci

.github/workflows/pythonpackage.yml

@@ -41,6 +41,10 @@ jobs:
       - name: Install dependencies
         run: poetry install
         if: steps.cached-poetry-dependencies.outputs.cache-hit != 'true'
+      - name: Run mypy
+        run: |
+          source $VENV
+          mypy .
       - name: Test with pytest
         run: |
           source $VENV