Enable incremental.

.github/workflows/pythonpackage.yml

@@ -47,7 +47,7 @@ jobs:
     - name: Install mypy
       run: |
         pip install -U mypy
-        python -m mypy --install-types
+        python -m mypy --install-types --incremental
       if: "matrix.python-version != 'pypy3'"
     - name: Style checks
       run: |