libubox: set abi version to previous bump for stable release

libubox: set abi version to previous bump for stable release

In order to keep a coherent set of dependencies of the packages in the
target specific packages (nonshared) in the stable 25.12.0 release
repositories and keep ImageBuilders and ASU functional, hard code the
abi-version used in that builbot phase1 run: "20260213".
*abi compatibility has not changed between 20260213 and 20260313 anyway.

Fixes: 8aac058ef0a58f394a920e5c39ac0390363c18f9 ("libubox: update to Git HEAD (2026-03-13)")
Suggested-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Mario Andrés Pérez <mapb_@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/22437
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>