Bump third_party/ot-br-posix/repo from `bd15f71` to `626b3f5` #1563

Job	Run time
Build on Darwin (clang, python_lib, simulated)	2h 49m 32s
Build on Linux (fake, gcc_release, clang, simulated)	2h 9m 30s
Build on Linux (coverage)	16m 32s
Build on Linux (gcc_debug)	1h 14m 11s
Build on Linux (python_lib)	32m 30s
Build on Linux (python lighting-app)	10m 24s
	7h 12m 39s

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