Tests

Bump third_party/openthread/repo from `eaa6261` to `af5938e` #1956

Job	Run time
REPL Tests - Linux	34m 6s
Test Suites - Darwin (no-ble-asan-clang)	1h 32m 42s
Test Suites - Linux (no-ble-tsan-clang)	1h 22m 23s
Test Suites - Darwin (no-ble-tsan-clang)	1h 53m 2s
REPL Tests - Darwin	0s
	5h 22m 13s

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