Bump third_party/ot-br-posix/repo from `bd15f71` to `952fc6a` #407

Job	Run time
Unit / Integration Tests (main)	16m 5s
Unit / Integration Tests (clang)	16m 52s
Unit / Integration Tests (mbedtls)	15m 49s
Unit / Integration Tests (rotating_device_id)	17m 36s
Unit / Integration Tests (icd)	45m 19s
	1h 51m 41s

Provide feedback