test: mark test-fs-readdir-ucs2 flaky

PR-URL: #13989
Reviewed-By: Refael Ackermann <[email protected]>

Author: joaocgreis

test/parallel/parallel.status

@@ -13,6 +13,7 @@ prefix parallel
 [$system==macos]
 
 [$arch==arm || $arch==arm64]
+test-fs-readdir-ucs2 : PASS,FLAKY
 
 [$system==solaris] # Also applies to SmartOS
 test-debug-signal-cluster         : PASS,FLAKY