Don't block the event loop on context end

Previously setTimeout (and co) might block the event loop in cases where
timeout hasn't triggered but the context has been done.

timers/timers.go

@@ -212,10 +212,13 @@ func (e *Timers) closeTaskQueue() {
 	// so that we do not execute it twice
 	e.taskQueueCh = nil
 
-	// wait for this to happen so we don't need to hit the event loop again
-	// instead this just closes the queue
-	ch <- struct{}{}
-	<-ch
+	select {
+	case ch <- struct{}{}:
+		// wait for this to happen so we don't need to hit the event loop again
+		// instead this just closes the queue
+		<-ch
+	case <-e.vu.Context().Done(): // still shortcircuit if the context is done as we might block otherwise
+	}
 }
 
 func (e *Timers) setupTaskQueueCloserOnIterationEnd() {