converters/simdutf: update to 5.2.6

Changelog: https://github.com/simdutf/simdutf/releases/tag/v5.2.4
Changelog: https://github.com/simdutf/simdutf/releases/tag/v5.2.5
Changelog: https://github.com/simdutf/simdutf/releases/tag/v5.2.6

MFH: 2024Q2
(cherry picked from commit 22772e8619046f43975698781b3b9259c0047d0b)