Bump third_party/ot-br-posix/repo from `bd15f71` to `5c66507` #410

Job	Run time
Unit / Integration Tests (main)	22m 4s
Unit / Integration Tests (clang)	21m 35s
Unit / Integration Tests (mbedtls)	21m 0s
Unit / Integration Tests (rotating_device_id)	22m 56s
Unit / Integration Tests (icd)	50m 3s
	2h 17m 38s

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