Bump third_party/openthread/repo from `aed9cd1` to `9277bce` #1971

Job	Run time
Unit / Integration Tests (main)	17m 51s
Unit / Integration Tests (clang)	17m 45s
Unit / Integration Tests (mbedtls)	16m 9s
Unit / Integration Tests (rotating_device_id)	16m 44s
Unit / Integration Tests (icd)	45m 34s
	1h 54m 3s

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