landlock.h: Fix printf format for size_t

It fixes warning on 32 bit:

include/lapi/landlock.h:134:56: warning: format '%lu' expects argument
of type 'long unsigned int', but argument 6 has type 'size_t' {aka
'unsigned int'}

Fixes: e441050 ("Added three more SAFE_* macros for landlock sandbox")
Signed-off-by: Petr Vorel <pvorel@suse.cz>

include/lapi/landlock.h

@@ -131,7 +131,7 @@ static inline int safe_landlock_create_ruleset(const char *file, const int linen
 	rval = tst_syscall(__NR_landlock_create_ruleset, attr, size, flags);
 	if (rval == -1) {
 		tst_brk_(file, lineno, TBROK | TERRNO,
-			"landlock_create_ruleset(%p, %lu, %u)",
+			"landlock_create_ruleset(%p, %zi, %u)",
 			attr, size, flags);
 	}