Bump third_party/ot-br-posix/repo from `bd15f71` to `952fc6a` #408

Job	Run time
Test Suites - Linux (no-ble-no-shell-tsan-clang)	2h 1m 14s
REPL Tests - Darwin	0s
REPL Tests - Linux	1h 34m 20s
Test Suites - Darwin (no-ble-no-shell-asan-clang)	1h 22m 38s
Test Suites - Darwin (no-ble-no-shell-tsan-clang)	2h 0m 53s
	6h 59m 5s

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