(PUP-3203) Don't mutate trigger when checking for equality

Previously, when checking if the current and desired triggers were
equivalent, we were silently deleting the index and enabled values from
the current trigger. If we later needed to delete the current
trigger, we would have lost its index, resulting in a call to
Win32::TaskScheduler.delete_trigger(nil) causing the error:

no implicit conversion from nil to integer

This commit ensure that we don't mutate the current or desired trigger.