Bump third_party/openthread/repo from `287dbfa` to `090c777` #1612

Job	Run time
Build on Darwin (clang, simulated)	45m 17s
Build on Linux (fake, gcc_release, clang, simulated)	52m 50s
Build on Linux (coverage)	13m 36s
Build on Linux (gcc_debug)	1h 4m 7s
Build on Linux (python_lib)	23m 44s
Build on Linux (python lighting-app)	6m 6s
	3h 25m 40s

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