libxml2: ignore disputed CVE-2023-45322

This CVE is a use-after-free which theoretically can be an exploit
vector, but this UAF only occurs when malloc() fails.  As it's
unlikely that the user can orchestrate malloc() failures at just the
place to break on _this_ malloc and not others it is disputed that this
is actually a security issue.

The underlying bug has been fixed, and will be incorporated into the
next release.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>