Bump third_party/ot-br-posix/repo from `bd15f71` to `faac6e7` #1667

Job	Run time
Unit / Integration Tests (main)	16m 20s
Unit / Integration Tests (clang)	20m 10s
Unit / Integration Tests (mbedtls)	17m 22s
Unit / Integration Tests (rotating_device_id)	16m 58s
Unit / Integration Tests (icd)	45m 57s
	1h 56m 47s

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