devel/*libplist: Update to 2.6.0

https://github.com/libimobiledevice/libplist/releases/tag/2.3.0
https://github.com/libimobiledevice/libplist/releases/tag/2.4.0
https://github.com/libimobiledevice/libplist/releases/tag/2.5.0
https://github.com/libimobiledevice/libplist/releases/tag/2.6.0

PR: 280014
Reported by: <fabio.comolli@gmail.com>