[Klipper ModelTest] Fix build

Fails to build with undefined reference to
bool QTest::qCompare<int, unsigned int>(int const&, unsigned int const&, char const*, char const*, char const*, int)'
error.

This has been fixed in 2f22f0a9 for 5.10 branch but not 5.8

Differential Revision: https://phabricator.kde.org/D6874