fs/proc: do_task_stat: use __for_each_thread()

mainline inclusion
from mainline-v6.7-rc1
commit 7904e53ed5a20fc678c01d5d1b07ec486425bb6a
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9E2EL
CVE: CVE-2024-26686

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7904e53ed5a20fc678c01d5d1b07ec486425bb6a

--------------------------------

do/while_each_thread should be avoided when possible.

Link: https://lkml.kernel.org/r/20230909164501.GA11581@redhat.com


Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Zhao Wenhui <zhaowenhui8@huawei.com>