test: mark test-performance-eventloopdelay flaky

Refs: #41286

This is one of the remaining high indicende failures
in the CI. Mark as flaky while it is investigated.

Signed-off-by: Michael Dawson <mdawson@devrus.com>

PR-URL: #41409
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/sequential/sequential.status

@@ -29,3 +29,7 @@ test-buffer-creation-regression: SKIP
 test-perf-hooks: SKIP
 
 [$arch==arm]
+
+[$arch==s390x]
+# https://github.com/nodejs/node/issues/41286
+test-performance-eventloopdelay: PASS, FLAKY