Bump third_party/openthread/repo from `f0b6fce` to `5e34ab2` #2303

Job	Run time
Build on Linux (fake, gcc_release, clang, simulated)	2h 11m 9s
Build on Darwin (clang, python_lib, simulated)	1h 53m 41s
Build on Linux (coverage)	16m 54s
Build on Linux (gcc_debug)	1h 13m 14s
Build on Linux (python_lib)	26m 39s
Build on Linux (python lighting-app)	6m 50s
	6h 8m 27s

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