test: mark test-cluster-shared-leak flaky

test-cluster-shared-leak is flaky on Windows.

Refs: https://github.com/nodejs/node/issues/3956

PR-URL: https://github.com/nodejs/node/pull/4162
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Roman Klauke <romaaan.git@gmail.com>
Reviewed-By: Minwoo Jung <jmwsoft@gmail.com>

test/parallel/parallel.status

@@ -7,9 +7,10 @@ prefix parallel
 [true] # This section applies to all platforms
 
 [$system==win32]
+test-child-process-fork-regr-gh-2847 : PASS,FLAKY
 test-cluster-net-send                : PASS,FLAKY
+test-cluster-shared-leak             : PASS,FLAKY
 test-tls-ticket-cluster              : PASS,FLAKY
-test-child-process-fork-regr-gh-2847 : PASS,FLAKY
 
 [$system==linux]
 test-http-client-timeout-event       : PASS,FLAKY