security/vuxml: document vulnerability in expat < 2.4.9

Rhodri James discovered a heap use-after-free vulnerability in the
doContent function in Expat, an XML parsing C library, which could
result in denial of service or potentially the execution of arbitrary
code, if a malformed XML file is processed.

https://www.debian.org/security/2022/dsa-5236
https://nvd.nist.gov/vuln/detail/CVE-2022-40674

Security: CVE-2022-40674