fix: Target Fedora 40 for official images, revert 39 to ci-test #809

Job	Run time
main image (silverblue, 37, nokmods)	8m 6s
main image (silverblue, 37, kmods)	12m 40s
main image (silverblue, 38, nokmods)	4m 8s
main image (silverblue, 38, kmods)	6m 49s
main image (silverblue, 39, nokmods)	5m 37s
main image (kinoite, 37, nokmods)	8m 14s
main image (kinoite, 37, kmods)	9m 10s
main image (kinoite, 38, nokmods)	6m 26s
main image (kinoite, 38, kmods)	8m 6s
main image (kinoite, 39, nokmods)	7m 0s
main image (sericea, 38, nokmods)	12m 57s
main image (sericea, 38, kmods)	48m 44s
main image (sericea, 39, nokmods)	4m 31s
main image (onyx, 39, nokmods)	6m 18s
main image (base, 37, nokmods)	2m 13s
main image (base, 37, kmods)	16m 14s
main image (base, 38, nokmods)	4m 8s
main image (base, 38, kmods)	7m 36s
main image (base, 39, nokmods)	5m 45s
main image (lxqt, 37, nokmods)	6m 58s
main image (lxqt, 37, kmods)	10m 21s
main image (lxqt, 38, nokmods)	7m 35s
main image (lxqt, 38, kmods)	9m 54s
main image (lxqt, 39, nokmods)	7m 6s
main image (mate, 37, nokmods)	10m 37s
main image (mate, 37, kmods)	9m 36s
main image (mate, 38, nokmods)	6m 2s
main image (mate, 38, kmods)	9m 9s
main image (mate, 39, nokmods)	8m 2s
main image (vauxite, 37, nokmods)	4m 42s
main image (vauxite, 37, kmods)	13m 8s
main image (vauxite, 38, nokmods)	7m 58s
main image (vauxite, 38, kmods)	9m 3s
main image (vauxite, 39, nokmods)	5m 9s
Check all builds successful	0s
	5h 10m 2s

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