ci: fix qt-6.8 workflow #15

Job	Run time
Build Release / flatpak	2m 30s
Build Release / build (ubuntu-20.04, 5, linux, 5.12.8, qtnetworkauth)	7m 36s
Build Release / build (ubuntu-20.04, 6, linux, 6.2.4, qt5compat qtimageformats qtnetworkauth)	11m 38s
Build Release / Nix (x86_64-linux)	13m 7s
Build Release / build (windows-2022, Windows-MinGW-w64, clang64, amd64_x86)	21m 5s
Build Release / Nix (x86_64-darwin)	14m 51s
Build Release / build (windows-2022, Windows-MSVC, x64, amd64, 6, windows, win64_msvc2022_64, 6.8.0, qt5compat qt...	15m 2s
Build Release / Nix (aarch64-darwin)	8m 54s
Build Release / build (windows-2022, Windows-MSVC-arm64, arm64, amd64_arm64, 6, windows, win64_msvc2019_arm64, 6....	15m 9s
Build Release / build (macos-14, macOS, 11, 6, mac, 6.8.0, qt5compat qtimageformats qtnetworkauth)	10m 43s
Build Release / build (macos-14, macOS-Legacy, 10.13, 5, mac, 5.15.2, qtnetworkauth)	5m 8s
create_release	1m 1s
	2h 6m 44s

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