Bump third_party/openthread/repo from `287dbfa` to `3560870` #2426

Job	Run time
REPL Tests - Darwin	0s
REPL Tests - Linux	1h 59m 18s
Test Suites - Linux (no-ble-no-shell-tsan-clang)	1h 45m 22s
Test Suites - Darwin (no-ble-no-shell-asan-clang)	1h 34m 52s
Test Suites - Darwin (no-ble-no-shell-tsan-clang)	1h 47m 19s
	7h 6m 51s

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