Update to Qt 6.8 (#164) #491

Job	Run time
prepare_matrix	6s
Cross platform build (Windows-msvc2022, windows-2022, msvc-2022, 17, MD, Release)	7m 3s
Cross platform build (Linux_gcc13, ubuntu-24.04, gcc, g++, gcc, 13, Release, Linux, libstdc++11, ...	5m 59s
Cross platform build (Macos_xcode14.3, macos-13, apple-clang, 14, Release, Macos, 14.3, libc++, x...	7m 25s
Cross platform build (Macos_xcode16, macos-15, apple-clang, 16, Release, Macos, 16.2, libc++, armv8)	5m 57s
	26m 30s

Provide feedback