test: mark test-trace-events-fs-sync as flaky

test-trace-events-fs-sync has been failing ocasinally on FreeBSD. While
we don't have a fix, it should be marked as flaky.

Ref: #21038

PR-URL: #21039
Refs: #21038
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Refael Ackermann <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Anatoli Papirovski <[email protected]>
Reviewed-By: Lance Ball <[email protected]>

Author: Matheus Marchini

test/parallel/parallel.status

@@ -20,5 +20,7 @@ test-child-process-fork-net: PASS,FLAKY
 [$system==solaris] # Also applies to SmartOS
 
 [$system==freebsd]
+# https://github.com/nodejs/node/issues/21038
+test-trace-events-fs-sync: PASS,FLAKY
 
 [$system==aix]