submodule: bump third_party/openthread/repo from `ae5b750` to `473af53` #5351

Job	Run time
Border Router (mDNSResponder)	29m 24s
Border Router (Avahi)	29m 50s
Border Router TREL (mDNSResponder)	28m 57s
Border Router TREL (Avahi)	29m 22s
Border Router MATN (mDNSResponder)	18m 22s
Border Router Internet Access Features (mDNSResponder)	26m 26s
Backbone Router	17m 46s
Border Router TREL with FEATURE_FLAG (avahi)	29m 37s
	3h 29m 44s

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