devel/json-c: Update to newer snapshot (81092b3)

• Remove my LOCAL from MASTER_SITES
• Bump PORTREVISION for package change

It includes various bug fixes and stability improvements.

Changes: https://github.com/json-c/json-c/commits/master

PR: 296904
Approved by: blanket (fix runtime)
MFH: 2026Q3
(cherry picked from commit 4d1473d5bc26dc20b1a62f040d863afd5c6a54d8)