checker: Allow non-three-letter task codes

def get_task(string: str) -> Tuple[str, str]:

    assert len(string) >= 7, "Teacher solution could not be parsed correctly."

    assert '-' in string, "Teacher solution could not be parsed correctly."

    teacher_type, task = string.split("-", 1)

    if len(task) > 3:

    if '-' in task:

        task, _ = task.split("-", 1)

    assert len(teacher_type) == 3 and len(task) == 3, "Teacher solution could not be parsed correctly."

    assert len(teacher_type) != 0, "Teacher solution code must not ne empty"

    assert len(task) != 0, "Task code must not be empty"

    return (teacher_type, task)