PyType step in CI is a no-op (echo instead of running pytype) #1917

Problem

The PyType step in the build job of .github/workflows/pythonapp.yml is:

- name: PyType
  run: |
    echo $(pwd)/runtests.sh --pytype

echo only prints the command; it never runs pytype. So static type checking has silently been disabled in CI.

Why it's hard to just turn on

runtests.sh --pytype runs pytype over the whole monailabel package with strict settings (check_attribute_types, check_container_types, check_parameter_types). Because it has never run in CI, there is a backlog of pre-existing type errors. Simply removing the echo would make the build job fail on those unrelated errors.

Suggested fix

1. Turn the step into a real $(pwd)/runtests.sh --pytype.
2. Triage and fix the pre-existing pytype errors (or reduce the strictness / scope) in the same change.

Filed separately from the fix so the type-error backlog can be addressed without blocking unrelated PRs.