python3-Cython: fix memory leak + debug output for generators #41948

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Job	Run time
Lint templates	41s
Build packages (x86_64, x86_64, glibc, linux/amd64, 1)	5m 33s
Build packages (i686, i686, glibc, linux/386, 1)	6m 46s
Build packages (aarch64, x86_64, glibc, linux/amd64, 0)	9m 17s
Build packages (armv7l, x86_64, glibc, linux/amd64, 0)	7m 18s
Build packages (x86_64-musl, x86_64-musl, musl, linux/amd64, 1)	5m 27s
Build packages (armv6l-musl, x86_64-musl, musl, linux/amd64, 0)	8m 35s
Build packages (aarch64-musl, x86_64-musl, musl, linux/amd64, 0)	7m 35s
	51m 12s

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