locking/lockdep: Add a test for lockdep_set_subclass()

Add a test case to ensure that no new name string literal will be
created in lockdep_set_subclass(), otherwise a warning will be triggered
in look_up_lock_class(). Add this to catch the problem in the future.

[boqun: Reword the title, replace #if with #ifdef and rename functions
and variables]

Signed-off-by: Ahmed Ehab <bottaawesome633@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/lkml/20240905011220.356973-1-bottaawesome633@gmail.com/