Bump third_party/openthread/repo from `287dbfa` to `147de7e` #369

Job	Run time
Unit / Integration Tests (main)	20m 23s
Unit / Integration Tests (clang)	16m 38s
Unit / Integration Tests (mbedtls)	17m 44s
Unit / Integration Tests (rotating_device_id)	17m 13s
Unit / Integration Tests (icd)	45m 33s
	1h 57m 31s

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