Bump third_party/openthread/repo from `aed9cd1` to `9277bce` #1972

Job	Run time
Build on Darwin (clang, python_lib, simulated)	2h 9m 45s
Build on Linux (coverage)	18m 31s
Build on Linux (fake, gcc_release, clang, simulated)	2h 5m 52s
Build on Linux (gcc_debug)	1h 6m 26s
Build on Linux (python_lib)	30m 5s
Build on Linux (python lighting-app)	10m 33s
	6h 21m 12s

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