test: set crypto-timing test as flaky

PR-URL: nodejs#50232
Refs: nodejs#38226
Reviewed-By: Ruy Adorno <ruyadorno@google.com>
Reviewed-By: Filip Skokan <panva.ip@gmail.com>

Author: anonrig

test/pummel/pummel.status

@@ -31,3 +31,7 @@ test-heapsnapshot-near-heap-limit: PASS,FLAKY
 [$system==ibmi]
 # https://github.com/nodejs/node/issues/39683
 test-regress-GH-892: PASS, FLAKY
+
+[$arch==s390x]
+# https://github.com/nodejs/node/issues/38226
+test-crypto-timing-safe-equal-benchmarks: PASS,FLAKY