docs: ja_JP/howto: Catch up update in v6.8

Catch up the update made in commit e49ad853

 ("CREDITS, MAINTAINERS,
docs/process/howto: Update man-pages' maintainer").

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Tsugikazu Shibata <shibata@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240502085610.111739-1-akiyks@gmail.com