selftests/bpf: Add bench test to arm64 and s390x denylist

BPF CI fails for arm64 and s390x each with the following result:

  [...]
  All error logs:

  serial_test_kprobe_multi_bench_attach:PASS:get_syms 0 nsec
  serial_test_kprobe_multi_bench_attach:PASS:kprobe_multi_empty__open_and_load 0 nsec
  libbpf: prog 'test_kprobe_empty': failed to attach: Operation not supported
  serial_test_kprobe_multi_bench_attach:FAIL:bpf_program__attach_kprobe_multi_opts unexpected error: -95
  #92      kprobe_multi_bench_attach:FAIL
  [...]

Add the test to the deny list.

Fixes: 5b6c7e5c ("selftests/bpf: Add attach bench test")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>