Common markdown styles usually show 4-column indents to separate the
list marker and the list item text.  That's a common template for
writing new markdown files.

On the other hand, we do have some files (such as CHANGES.md) where we
use a different style.

From a markdown perspective, both are perfectly OK, and there's no
reason to enforce either.

Therefore, the best thing is to exclude this particular rule.

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #18297)

(cherry picked from commit 2046f80)