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: de7b9927

 ("selftests/bpf: Add test for prealloc_lru_pop bug")
Signed-off-by: Daniel Müller <deso@posteo.net>
Acked-by: Mykola Lysenko <mykolal@fb.com>
Link: https://lore.kernel.org/r/20220810200710.1300299-1-deso@posteo.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>