selftests/landlock: Add tests for invalid use of quiet flag

Make sure that these calls return EINVAL.

Test coverage for security/landlock is 91.6% of 2347 lines according to
LLVM 22.

Assisted-by: GitHub-Copilot:claude-opus-4.8
Signed-off-by: Tingmao Wang <m@maowtm.org>
Link: https://patch.msgid.link/9401d5c6468675863d944d6c26640d97db1a1f31.1781228815.git.m@maowtm.org
[mic: Add test coverage]
Signed-off-by: Mickaël Salaün <mic@digikod.net>