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Fix findChild/findChildren logic: #746

Job	Run time
oldschool (rockylinux, 9, debug)	10s
windows (win64_msvc2017_64, 3.6, x64, 5.11.*)	59s
macOS (latest, 3.11, 5.12.*, debug)	10s
windows (win64_msvc2019_64, 3.13, x64, 5.15.*, PythonQtCore PythonQtGui PythonQtMultimedia)	1m 0s
macOS (latest, 3.9, 5.9.*, release)	8s
macOS (latest, 3.9, 5.9.*, debug)	55s
oldschool (rockylinux, 9, release)	10s
ubuntu (24.04)	1m 4s
windows (win64_mingw73, 3.10, 5.12.*, x64)	59s
ubuntu (22.04)	55s
windows (win32_mingw53, 3.6, x86, 5.11.*)	1m 0s
	7m 30s

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