Bump third_party/ot-br-posix/repo from `bd15f71` to `af26b01` #590

Job	Run time
REPL Tests - Darwin	0s
REPL Tests - Linux	55m 33s
Test Suites - Darwin (no-ble-asan-clang)	1h 18m 6s
Test Suites - Darwin (no-ble-tsan-clang)	1h 48m 28s
Test Suites - Linux (no-ble-tsan-clang)	1h 29m 42s
	5h 31m 49s

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