chore: properly clean up schedules in tests

[chris-olszewski]

What was changed

• Save schedule ids incrementally. Previously if one of these schedule creations failed we would not track the schedule id and be unable to clean it up causing future tests's assert_no_schedules! calls to fail.
• Switch from using defined?(handle) as the guard for schedule cleanup to just checking if the handle is present. (defined?(handle) will always be true regardless of if we have schedules or not)

Why?

I had test_calendar_spec_defaults fail due to schedules from other tests not being cleaned up.

Checklist

1. Closes N/A

2. How was this tested:
   CI

3. Any docs updates needed?
   N/A