Darwin: mark `copyPublicKey` as `CF_RETURNS_RETAINED` #112352

Job	Run time
Build on Linux (fake, gcc_release, clang, simulated)	57m 24s
Build on Linux (fake, gcc_release, clang, simulated)	57m 24s
Build on Linux (gcc_debug)	1h 8m 15s
Build on Linux (gcc_debug)	1h 8m 15s
Build on Darwin (clang, simulated)	39m 40s
Build on Darwin (clang, simulated)	53m 30s
Build on Linux (coverage)	19m 13s
Build on Linux (coverage)	19m 13s
Build on Linux (python_lib)	29m 12s
Build on Linux (python_lib)	29m 12s
Build on Linux (python lighting-app)	11m 12s
Build on Linux (python lighting-app)	11m 12s
	7h 43m 42s

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