textproc/fcitx5-configtool: fix plist against KDE Frameworks 5.110

The change [1] in KDE Frameworks leads to the configuration
ecm_setup_version(PROJECT VARIABLE_PREFIX Fcitx5Migrator

VERSION_HEADER "${CMAKE_CURRENT_BINARY_DIR}/migrator_version.h"
PACKAGE_VERSION_FILE "${CMAKE_CURRENT_BINARY_DIR}/Fcitx5MigratorVersion.cmake"
SOVERSION 0)

accepting the value '0' as so-version, and not defaulting to the
softwares major version (here 5).

This leads to the .so.5 being renamed to .so.0 in the final package.

[1] https://invent.kde.org/frameworks/extra-cmake-modules/-/commit/1da0bba97d170e6d04eaf5555681c1b325cabcf5

PR: 273695