Qt6: Empty BUNDLE_INSTALL_DIR
BUNDLE_INSTALL_DIR is not set when KDEInstallDirs6 is used.
Apparently it is caused by KDE_INSTALL_DIRS_NO_DEPRECATED=TRUE
# on the Mac support an extra install directory for application bundles
if(APPLE)
set(KF_INSTALL_TARGETS_DEFAULT_ARGS ${KF_INSTALL_TARGETS_DEFAULT_ARGS}
BUNDLE DESTINATION "${BUNDLE_INSTALL_DIR}" )
endif()