devel/serd: Update 0.32.6 => 0.32.8

Changelog:
https://gitlab.com/drobilla/serd/-/releases/v0.32.8

PR: 294386
Reported by: Goran Mekić <meka@tilda.center> (maintainer)
Approved by: osa (mentor)
MFH: 2026Q2

(cherry picked from commit e5fe730121cc4d9a3f519e4f7596a92da54cc32d)