submodule: bump openthread from `830572f` to `4a9fb06` #958

Job	Run time
cancel-previous-runs	8s
Test Suite network-forming	33m 48s
Test Suite commissioning	13m 54s
Test Suite connectivity	22m 22s
Test Suite network-latency	2m 37s
Test Suite multicast-performance	2m 45s
Test Suite otns-performance	3m 37s
Test Suite network-limits	3m 34s
	1h 22m 45s

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