Bump third_party/openthread/repo from `287dbfa` to `9f9d0a5` #2461

Job	Run time
REPL Tests - Linux	7m 16s
Test Suites - Darwin (no-ble-no-shell-asan-clang)	1h 30m 56s
Test Suites - Linux (no-ble-no-shell-tsan-clang)	5m 36s
Test Suites - Darwin (no-ble-no-shell-tsan-clang)	1h 56m 6s
REPL Tests - Darwin	0s
	3h 39m 54s

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