selftests/landlock: Fix makefile header list

Make all headers part of make's dependencies computations.
Otherwise, updating audit.h, common.h, scoped_base_variants.h,
scoped_common.h, scoped_multiple_domain_variants.h, or wrappers.h,
re-running make and running selftests could lead to testing stale headers.

Fixes: 6a500b22 ("selftests/landlock: Add tests for audit flags and domain IDs")
Fixes: fefcf0f7 ("selftests/landlock: Test abstract UNIX socket scoping")
Fixes: 5147779d ("selftests/landlock: Add wrappers.h")
Signed-off-by: Matthieu Buffet <matthieu@buffet.re>
Link: https://lore.kernel.org/r/20251027011440.1838514-1-matthieu@buffet.re


Signed-off-by: Mickaël Salaün <mic@digikod.net>