zio: do no-op injections just before handing off to vdevs

The purpose of no-op is to simulate a failure between a device cache and
its permanent store. We still want it to go through the queue and
respond in the same way to everything else.

So, inject "success" as the very last thing, and then move on to
VDEV_IO_DONE to be dequeued and so any followup work can occur.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #17029