[flink][test] make orphan segment dir old to fix empty-dir sweep assertion

BucketCleaner only sweeps empty directories whose mtime is older than the
cutoff. createOldSegmentFile was making the file old but leaving the parent
directory at 'now', so the post-order sweep skipped it. Add makeOld on the
directory to match production reality.

Author: platinumhamburg

fluss-flink/fluss-flink-common/src/test/java/org/apache/fluss/flink/action/orphan/OrphanFilesCleanITCase.java

@@ -887,6 +887,7 @@ private Path createOldSegmentFile(TablePath tablePath, String fileName) throws E
         Path file = segmentDir.resolve(fileName);
         Files.write(file, new byte[] {0x42});
         makeOld(file);
+        makeOld(segmentDir);
         return file;
     }