Bump third_party/openthread/repo from `aed9cd1` to `db63932` #282

Job	Run time
Build on Darwin (clang, python_lib, simulated)	2h 1m 52s
Build on Linux (coverage)	14m 6s
Build on Linux (fake, gcc_release, clang, simulated)	1h 57m 24s
Build on Linux (gcc_debug)	1h 1m 56s
Build on Linux (python_lib)	29m 31s
Build on Linux (python lighting-app)	6m 58s
	5h 51m 47s

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