Bump third_party/ot-br-posix/repo from `c5a7a35` to `9bdaa91` #91143

Job	Run time
Build on Linux (fake, gcc_release, clang, simulated)	1h 27m 45s
Build on Darwin (clang, python_lib, simulated)	1h 58m 54s
Build on Linux (gcc_debug)	47m 53s
Build on Linux (coverage)	10m 4s
Build on Linux (python_lib)	20m 14s
Build on Linux (python lighting-app)	6m 0s
	4h 50m 50s

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