march: fix --no-traverse being very slow - fixes #8860

Before this change --no-traverse was calling NewObject on directories
(where it would always fail) as well as files. This was very
noticeable when doing syncs with --max-age which were only
transferring a small number of objects. This should have been very
quick, but the NewObject calls for each directory slowed the sync down
a lot.

This changes replaces the check to see if the source entry is an
Object that got missed out from this commit:

88e30eecbf march: fix deadlock when using --no-traverse - fixes #8656

fs/march/march.go

@@ -455,6 +455,11 @@ func (m *March) processJob(job listDirJob) ([]listDirJob, error) {
 			go func() {
 				defer workerWg.Done()
 				for t := range matchTasks {
+					// Can't match directories with NewObject
+					if _, ok := t.src.(fs.Object); !ok {
+						t.dstMatch <- nil
+						continue
+					}
 					leaf := path.Base(t.src.Remote())
 					dst, err := m.Fdst.NewObject(m.Ctx, path.Join(job.dstRemote, leaf))
 					if err != nil {