Bump third_party/ot-br-posix/repo from `bd15f71` to `faac6e7` #1478

Job	Run time
REPL Tests - Darwin	0s
Test Suites - Darwin (no-ble-no-shell-asan-clang)	1h 14m 19s
Test Suites - Linux (no-ble-no-shell-tsan-clang)	1h 43m 27s
Test Suites - Darwin (no-ble-no-shell-tsan-clang)	1h 53m 22s
REPL Tests - Linux	1h 54m 50s
	6h 45m 58s

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