denylist: Disable some tests temporarily for s390x.

These BPF selftests,

 - dummy_st_ops/dummy_init_ptr_arg,

 - fexit_bpf2bpf,

 - tailcalls,

 - trace_ext,

 - xdp_bpf2bpf, and

 - xdp_metadata,

cause acrashes on the s390x platform. [1] They should be disable
temporarily.

[1] https://lore.kernel.org/bpf/[email protected]/

Signed-off-by: Kui-Feng Lee <[email protected]>

Author: ThinkerYzu1

ci/vmtest/configs/DENYLIST.s390x

@@ -1,3 +1,11 @@
 deny_namespace                           # not yet in bpf denylist
 tc_redirect/tc_redirect_dtime            # very flaky
 lru_bug                                  # not yet in bpf-next denylist
+# Disabled temporarily for a crash.
+# https://lore.kernel.org/bpf/[email protected]/
+dummy_st_ops/dummy_init_ptr_arg
+fexit_bpf2bpf
+tailcalls
+trace_ext
+xdp_bpf2bpf
+xdp_metadata