www/srt: Update WWW
The previous commit for 1.5.6 resolved the following CVEs:
- CVE-2026-55869: Heap-Based Buffer Overflow in KMREQ Handling
- CVE-2026-55868: Encryption State Machine Downgrade
ChangeLog: https://github.com/Haivision/srt/releases/tag/v1.5.6
(cherry picked from commit 88c18f3c4026ce1b5bdf10c758e5ea31da414706)