test: set test-structuredclone-jstransferable non-flaky

Fixes: #50260
PR-URL: #54115
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>

Author: StefanStojanovic

test/pummel/pummel.status

@@ -9,8 +9,6 @@ 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==macos]