Describe the bug

Currently we are not allowed to edit dates for a checkpoint gradeable as #11539 adds a loadTemplate, which is not being rendered when we are on a checkpoint gradeable. In addition, we cannot edit a checkpoint gradeable due to #11702 because team lock date was wrong

Expected behavior

We should add more e2e tests editing checkpoint gradeables because they can differ from electronic gradeables

To Reproduce
Steps to reproduce the behavior:
Not a bug, but dates for checkpoint gradeables were broken at some point: the date page did not render at all. We should add E2E test to test checkpoint gradeables in general, just like we are doing for electronic ones.

Configuration

• OS: [e.g. Windows, Linux, ...]
• Browser [e.g. Chrome, Safari]

Screenshots

Additional context