cgroup: Fixes for v7.1-rc6

One cpuset fix and a maintenance update, both low-risk:

- Fix cpuset partition CPU accounting under sibling CPU exclusion that could
  produce wrong CPU assignments and trigger scheduling-domain warnings.
  Includes selftests.

- Update an email address in MAINTAINERS.

cgroup/cpuset: Change Ridong's email

The chenridong@huaweicloud.com is no longer a valid email,
replace it with the personal email ridong.chen@linux.dev

Signed-off-by: Ridong Chen <ridong.chen@linux.dev>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>