Fix irritatingly wrong version number for Qt6 #317

Job	Run time
oldschool (centos, 7, python-debug, debug)	4m 47s
ubuntu (20.04)	22m 59s
windows (win64_mingw73, 3.10, 5.12.*, x64)	6m 44s
ubuntu (22.04)	18m 2s
oldschool (centos, 7, python-debug, release)	5m 24s
macOS (11, 3.6, 5.9.*, release)	14m 10s
windows (win64_msvc2017_64, 3.6, x64, 5.11.*)	4m 54s
oldschool (rockylinux, 9, python3-devel, release)	4m 40s
macOS (11, 3.6, 5.9.*, debug)	6m 0s
windows (win32_mingw53, 3.6, x86, 5.11.*)	7m 31s
macOS (12, 3.11, 5.12.*, debug)	5m 18s
	1h 40m 29s

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