submodule: bump openthread from `830572f` to `473af53` #985

Job	Run time
cancel-previous-runs	6s
Test Suite network-forming	22m 26s
Test Suite commissioning	8m 57s
Test Suite connectivity	22m 54s
Test Suite network-latency	2m 17s
Test Suite multicast-performance	2m 4s
Test Suite otns-performance	2m 7s
Test Suite network-limits	2m 1s
	1h 2m 52s

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