storage: un-starve TestReplicateQueueDownReplicate

Before this change,

> make test PKG=./pkg/storage/ TESTS=TestReplicateQueueDownReplicate
> TESTFLAGS='-count 10'

takes ~109s on my laptop. After this change, it takes ~18s.

This is in line with a test failure on CI which looked like the test
had just never managed to schedule the goroutines that matter in time
for things to wrap up.

Fixes cockroachdb#32256.

Release note: None

pkg/storage/replicate_queue_test.go

@@ -194,8 +194,8 @@ func TestReplicateQueueDownReplicate(t *testing.T) {
  base.TestClusterArgs{
  ReplicationMode: base.ReplicationAuto,
  ServerArgs: base.TestServerArgs{
- ScanMinIdleTime: time.Millisecond,
- ScanMaxIdleTime: time.Millisecond,
+ ScanMinIdleTime: 10 * time.Millisecond,
+ ScanMaxIdleTime: 10 * time.Millisecond,
  Knobs: base.TestingKnobs{
  Store: &storage.StoreTestingKnobs{
  // Prevent the merge queue from immediately discarding our splits.