Bump third_party/ot-br-posix/repo from `bd15f71` to `7fd5bd1` #430

Job	Run time
Unit / Integration Tests (main)	15m 54s
Unit / Integration Tests (clang)	16m 37s
Unit / Integration Tests (mbedtls)	17m 1s
Unit / Integration Tests (rotating_device_id)	26m 25s
Unit / Integration Tests (icd)	45m 39s
	2h 1m 36s

Provide feedback