Use Qt 6.8.0 as the Qt6 version in IFW tests

Update Jenkins variables for 'ifw_qt6' to 6.8.0:

IFW_QT6

IFW_QT6_BRANCH

Also check the configurations, there might be some needs for update, e.g the linux on arm target changes from Debian11.6 to Ubuntu24.04, and there is cross compiled windows on arm target: win-msvc2022-Windows11-23H2-x64_msvc2022-arm64 (ask dev team does it need to be added, since there is native windows on arm)