Bump third_party/ot-br-posix/repo from `bd15f71` to `5c66507` #5553

Job	Run time
Build on Darwin (clang, simulated)	47m 12s
Build on Linux (fake, gcc_release, clang, simulated)	52m 40s
Build on Linux (coverage)	15m 36s
Build on Linux (gcc_debug)	1h 4m 42s
Build on Linux (python_lib)	24m 21s
Build on Linux (python lighting-app)	7m 10s
	3h 31m 41s

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