selftests/bpf: Add kprobe_multi override test

Adding test that tries to attach program with bpf_override_return
helper to function not within error injection list.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230907200652.926951-2-jolsa@kernel.org