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Bump third_party/ot-br-posix/repo from `bd15f71` to `277c9e0` #927

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Job	Run time
Chef - ESP32 CI Examples	11m 52s
Chef - Linux CI Examples	4m 40s
Chef - NRFConnect CI Examples	9m 53s
Chef - Telink CI Examples	9m 35s
	36m 0s