test: mark test-dgram-multicast-ssmv6-multi-process flaky

refs: https://github.com/nodejs/node/issues/32946

Mark this test as flaky on linux
Ive used sequential.status as a template for this file

PR-URL: https://github.com/nodejs/node/pull/33498
Refs: https://github.com/nodejs/node/issues/32946


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>