Bump third_party/ot-br-posix/repo from `8299da3` to `1576ade` #5114

Job	Run time
REPL Tests - Linux	35m 44s
Test Suites - Darwin (no-ble-asan-clang)	1h 34m 1s
Test Suites - Darwin (no-ble-tsan-clang)	2h 5m 10s
Test Suites - Linux (no-ble-tsan-clang)	1h 46m 43s
REPL Tests - Darwin	0s
	6h 1m 38s

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