security/vuxml: document ffmpeg vulnerability

[smyru]

Summary

Approved by: 0mp (mentor)
Security: CVE-2026-8461

[diizzy]

Having a quick look, <p> section should be formatted and you can also remove the empty line.
https://cgit.freebsd.org/ports/tree/security/vuxml/vuln/2026.xml#n91
LGTM otherwise as long as validation tests passes and pkg version tests (not performed by me)

[smyru]

Address review comments

[fernape]

LGTM!

Thanks!