Bump third_party/ot-br-posix/repo from `bd15f71` to `3baf160` #278

Job	Run time
Unit / Integration Tests (main)	16m 7s
Unit / Integration Tests (clang)	17m 7s
Unit / Integration Tests (mbedtls)	17m 35s
Unit / Integration Tests (rotating_device_id)	16m 41s
Unit / Integration Tests (icd)	45m 54s
	1h 53m 24s

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