Bump third_party/openthread/repo from `287dbfa` to `bc54d67` #115486

Job	Run time
Build on Linux (fake, gcc_release, clang, simulated)	52m 41s
Build on Darwin (clang, simulated)	46m 8s
Build on Linux (coverage)	21m 15s
Build on Linux (gcc_debug)	56m 32s
Build on Linux (python_lib)	21m 34s
Build on Linux (python lighting-app)	7m 32s
	3h 25m 42s

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