fix flaky busy test (#20861)

* fix flaky busy test

* increase busy duration

app/busy_test.go

@@ -15,7 +15,6 @@ import (
 )
 
 func TestBusySet(t *testing.T) {
-	t.Skip("MM-45725")
 	cluster := &ClusterMock{Busy: &Busy{}}
 	busy := NewBusy(cluster)
 
@@ -25,11 +24,12 @@ func TestBusySet(t *testing.T) {
 
 	require.False(t, busy.IsBusy())
 
-	busy.Set(time.Millisecond * 100)
+	busy.Set(time.Millisecond * 500)
 	require.True(t, busy.IsBusy())
 	require.True(t, compareBusyState(t, busy, cluster.Busy))
-	// should automatically expire after 100ms.
-	require.Eventually(t, isNotBusy, time.Second*15, time.Millisecond*20)
+
+	// should automatically expire after 500ms.
+	require.Eventually(t, isNotBusy, time.Second*15, time.Millisecond*100)
 	// allow a moment for cluster to sync.
 	require.Eventually(t, func() bool { return compareBusyState(t, busy, cluster.Busy) }, time.Second*15, time.Millisecond*20)