unicode: kunit: change tests filename and path

Change utf8 kunit test filename and path to follow the style
convention on Documentation/dev-tools/kunit/style.rst

Co-developed-by: Pedro Orlando <porlando@lkcamp.dev>
Signed-off-by: Pedro Orlando <porlando@lkcamp.dev>
Co-developed-by: Danilo Pereira <dpereira@lkcamp.dev>
Signed-off-by: Danilo Pereira <dpereira@lkcamp.dev>
Signed-off-by: Gabriela Bittencourt <gbittencourt@lkcamp.dev>
Reviewed-by: David Gow <davidgow@google.com>
Acked-by: Gabriel Krisman Bertazi <krisman@suse.de>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Rae Moar <rmoar@google.com>
Link: https://lore.kernel.org/r/20241202075545.3648096-7-davidgow@google.com


Signed-off-by: Kees Cook <kees@kernel.org>