CMake: Fix sabotaged Landlock sandbox check.

It never enabled it.

CMakeLists.txt

@@ -1001,7 +1001,7 @@ if(NOT SANDBOX_FOUND AND ENABLE_SANDBOX MATCHES "^ON$|^landlock$")
         #include <linux/landlock.h>
         #include <sys/syscall.h>
         #include <sys/prctl.h>
-.
+
         void my_sandbox(void)
         {
             (void)prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);