selftests/bpf: Add lru_bug to s390x deny list

The lru_bug BPF selftest is failing execution on s390x machines. The
failure is due to program attachment failing in turn, similar to a bunch
of other tests. Those other tests have already been deny-listed and with
this change we do the same for the lru_bug test, adding it to the
corresponding file.

Fixes: de7b9927105b ("selftests/bpf: Add test for prealloc_lru_pop bug")
Signed-off-by: Daniel Müller <[e-mail]>
Acked-by: Mykola Lysenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/DENYLIST.s390x

···
 select_reuseport                         # intermittently fails on new s390x setup
 xdp_synproxy                             # JIT does not support calling kernel function                                (kfunc)
 unpriv_bpf_disabled                      # fentry
+lru_bug                                  # prog 'printk': failed to auto-attach: -524