Show diff. (#1663)

.github/workflows/build_and_test.yml

@@ -428,7 +428,7 @@ jobs:
         python -m pip install -U mypy pybind11-stubgen
         cd pytket
         ./stub_generation/regenerate_stubs
-        git diff --quiet pytket/_tket && echo "Stubs are up-to-date" || exit 1  # fail if stubs change after regeneration
+        git diff pytket/_tket && echo "Stubs are up-to-date" || exit 1  # fail if stubs change after regeneration
         python -m mypy --config-file=mypy.ini --no-incremental -p pytket -p tests
     - name: Upload package
       if: github.event_name == 'push' && needs.check_changes.outputs.tket_changed == 'true'