x11-toolkits/qt5-declarative-test: fix packaging

When x11-toolkits/qt5-declarative-test was split out of
x11-toolkits/qt5-declarative in 4d10eef66bb959ed0433df9e065458af4c325552 a handfull of
files got dropped unnoticed.

KDE's CI systems noticed this issue a while back as QtQuick test cases
would no longer work.

This change now again makes sure to install the QtQuick-Test related QML
files so that these should again work.

Reported by: KDE