Bump third_party/openthread/repo from `f0b6fce` to `5e34ab2` #1203

Job	Run time
Build on Darwin (clang, python_lib, simulated)	1h 47m 29s
Build on Linux (fake, gcc_release, clang, simulated)	2h 9m 39s
Build on Linux (coverage)	17m 18s
Build on Linux (gcc_debug)	1h 15m 21s
Build on Linux (python_lib)	31m 57s
Build on Linux (python lighting-app)	10m 47s
	6h 12m 31s

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