…shed (go-gitea#18593)

Backport go-gitea#18593

There is a possible race whereby a worker pool could be cancelled but yet the
underlying queue is not empty. This will lead to flush-all cycling because it
cannot empty the pool.

* On shutdown of Persistant Channel Queues close datachan and empty

Partial Backport go-gitea#18415

Although we attempt to empty the datachan in queues - due to
races we are better off just closing the channel and forcibly emptying
it in shutdown.

Fix go-gitea#18618

Signed-off-by: Andrew Thornton <art27@cantab.net>

Fix go-gitea#18617

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: Gusted <williamzijl7@hotmail.com>

Co-authored-by: Gusted <williamzijl7@hotmail.com>