docs: update dev-tools/kcsan.rst url about KTSAN

The KTSAN doc has moved to
https://github.com/google/kernel-sanitizers/blob/master/KTSAN.md

.
Update the url in kcsan.rst accordingly.

Signed-off-by: Haoyang Liu <tttturtleruss@hust.edu.cn>
Reviewed-by: Dongliang Mu <dzm91@hust.edu.cn>
Acked-by: Marco Elver <elver@google.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240725174632.23803-1-tttturtleruss@hust.edu.cn