selftests/landlock: Add binaries to .gitignore

Building the test creates binaries 'wait-pipe' and
'sandbox-and-launch' which need to be gitignore'd.

Signed-off-by: Bharadwaj Raju <bharadwaj.raju777@gmail.com>
Link: https://lore.kernel.org/r/20250210161101.6024-1-bharadwaj.raju777@gmail.com


[mic: Sort entries]
Signed-off-by: Mickaël Salaün <mic@digikod.net>