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Improve PYTHONQTALL_CONFIG env var handling for CMD #384

Job	Run time
ubuntu (20.04)	21m 29s
oldschool (centos, 7, python-debug, debug)	5m 49s
ubuntu (22.04)	18m 42s
windows (win64_mingw73, 3.10, 5.12.*, x64)	6m 37s
oldschool (centos, 7, python-debug, release)	5m 8s
macOS (11, 3.6, 5.9.*, release)	14m 20s
windows (win64_msvc2017_64, 3.6, x64, 5.11.*)	4m 55s
oldschool (rockylinux, 9, python3-devel, release)	4m 26s
macOS (11, 3.6, 5.9.*, debug)	6m 41s
windows (win64_msvc2019_64, 3.12, x64, 5.15.*, PythonQtCore PythonQtGui PythonQtMultimedia)	4m 44s
macOS (12, 3.11, 5.12.*, debug)	3m 21s
windows (win64_msvc2017_64, 3.6, x64, 5.11.*)	4m 44s
windows (win32_mingw53, 3.6, x86, 5.11.*)	7m 33s
	1h 48m 29s

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