MAINTAINERS: add Yang Yang as a co-maintainer of PER-TASK DELAY ACCOUNTING

Balbir Singh is the unique maintainer of PER-TASK DELAY ACCOUNTING, and he
had started work on cgroupstats a long time back, this subsystem then is
not growing at a very rapid pace. With their excellent work delay
accounting is still very useful for observing and optimizing system delay,
but still needs continuous improvement. Yang Yang with his team had
worked for most of the recent patches of the subsystem, and he has a
strong willing to help, Balbir Singh is glad to see that, so add him as a
co-maintainer.

Link: https://lkml.kernel.org/r/20250117222013817zWHgBaSigRI_eRJt1hqnu@zte.com.cn
Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
Cc: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>