test: set test-structuredclone-* as flaky

PR-URL: nodejs#50261
Refs: nodejs#50260
Reviewed-By: Zeyu "Alex" Yang <himself65@outlook.com>
Reviewed-By: Vinícius Lourenço Claro Cardoso <contact@viniciusl.com.br>

Author: anonrig

test/pummel/pummel.status

@@ -9,6 +9,8 @@ prefix pummel
 [$system==win32]
 # https://github.com/nodejs/node/issues/40728
 test-fs-watch-non-recursive: PASS,FLAKY
+# https://github.com/nodejs/node/issues/50260
+test-structuredclone-jstransferable: PASS,FLAKY
 
 [$system==linux]
 # https://github.com/nodejs/node/issues/38226