Properly flush unique queues on startup (#23154)

There have been a number of reports of PRs being blocked whilst being
checked which have been difficult to debug. In investigating #23050 I
have realised that whilst the Warn there is somewhat of a miscall there
was a real bug in the way that the LevelUniqueQueue was being restored
on start-up of the PersistableChannelUniqueQueue.

Next there is a conflict in the setting of the internal leveldb queue
name - This wasn't being set so it was being overridden by other unique
queues.

This PR fixes these bugs and adds a testcase.

Thanks to @brechtvl  for noticing the second issue.

Fix #23050
and others

---------

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

modules/queue/queue_channel.go

@@ -124,7 +124,10 @@ func (q *ChannelQueue) Shutdown() {
 		log.Trace("ChannelQueue: %s Flushing", q.name)
 		// We can't use Cleanup here because that will close the channel
 		if err := q.FlushWithContext(q.terminateCtx); err != nil {
-			log.Warn("ChannelQueue: %s Terminated before completed flushing", q.name)
+			count := atomic.LoadInt64(&q.numInQueue)
+			if count > 0 {
+				log.Warn("ChannelQueue: %s Terminated before completed flushing", q.name)
+			}
 			return
 		}
 		log.Debug("ChannelQueue: %s Flushed", q.name)