Prevent timer leaks in Workerpool and others (#11333)

There is a potential memory leak in `Workerpool` due to the intricacies of
`time.Timer` stopping.

Whenever a `time.Timer` is `Stop`ped its channel must be cleared using a
`select` if the result of the `Stop()` is `false`.

Unfortunately in `Workerpool` these were checked the wrong way round.

However, there were a few other places that were not being checked.

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

Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/queue/queue_wrapped.go

@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/util"
 )
 
 // WrappedQueueType is the type for a wrapped delayed starting queue
@@ -88,7 +89,7 @@ func (q *delayedStarter) setInternal(atShutdown func(context.Context, func()), h
 			t := time.NewTimer(sleepTime)
 			select {
 			case <-ctx.Done():
-				t.Stop()
+				util.StopTimer(t)
 			case <-t.C:
 			}
 		}