Tests

Bump third_party/ot-br-posix/repo from `bd15f71` to `277c9e0` #1477

Job	Run time
Test Suites - Linux (no-ble-no-shell-tsan-clang)	1h 44m 54s
Test Suites - Darwin (no-ble-no-shell-asan-clang)	1h 22m 39s
REPL Tests - Linux	1h 56m 13s
Test Suites - Darwin (no-ble-no-shell-tsan-clang)	1h 52m 25s
REPL Tests - Darwin	0s
	6h 56m 11s

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