Qt6HostInfo package loading fails if QT_REPO_MODULE_VERSION is not 6

bb4437e72487d9f35c4cc93bff6acefc71871c68 in qtqa changed QT_REPO_MODULE_VERSION to 1.0.0.

With that, qt5.git integrations for cross-compiling configs failed, because in QtSetup.cmake we do

    find_package(Qt${PROJECT_VERSION_MAJOR}HostInfo
                 CONFIG
                 REQUIRED
                 PATHS "${QT_HOST_PATH}"
                       "${QT_HOST_PATH_CMAKE_DIR}"
                 NO_CMAKE_FIND_ROOT_PATH
                 NO_DEFAULT_PATH)

which attempts to load Qt1HostInfo.

This was reverted in https://codereview.qt-project.org/c/qt/qtqa/+/330111

The find_package call above must not use PROJECT_VERSION_MAJOR but something else.

The top-level find_package calls also use PROJECT_VERSION_MAJOR:

find_package(Qt6 ${PROJECT_VERSION} CONFIG REQUIRED COMPONENTS BuildInternals Core Test) # special case
find_package(Qt6 ${PROJECT_VERSION} CONFIG OPTIONAL_COMPONENTS Gui Widgets) # special case

This is bound to break once the QT_REPO_MODULE_VERSION is greater than the Qt version. Regardless of cross-building or not.