libubox: update to Git HEAD (2025-12-08)

libubox: update to Git HEAD (2025-12-08)

5714bf6ae652 build: install libubox
440b4e988f39 tests: shunit2: add dump and setters coverage
a3ff29ef93df tests: shunit2: add test for _jshn_append via JSON script
38d70328ecbd github: ci: add MIPS64, PowerPC64 and RISCV64
edaf77da740d scripts: devel-build: add missing LUAPATH
c0773869c9d6 build: disable static json-c
ecddb31dc34d formal: fix workflow permissions
7928f1711703 libubox: Add ability to find ordinal position inside a table

Changes: https://github.com/openwrt/libubox/compare/a75209f62982f7218f73b9b4fd9b705e19f5f94a...7928f1711703767b0ac5ce916c7231d0e1af1ca2

Link: https://github.com/openwrt/openwrt/pull/21099
Signed-off-by: Hauke Mehrtens <[email protected]>