selftests/bpf: Fix spelling mistake "detecion" -> "detection"

There is a spelling mistake in a literal string. Fix it.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230206092229.46416-1-colin.i.king@gmail.com