submodule: bump third_party/openthread/repo from `499f668` to `70adca… #4632

Job	Run time
docker-check (UART)	6m 32s
docker-check (SPI)	5m 10s
buildx (latest, ubuntu:bionic, linux/amd64,linux/arm/v7,linux/arm64, yes)	38m 29s
buildx (focal, ubuntu:focal, linux/amd64,linux/arm64, yes)	25m 12s
buildx (jammy, ubuntu:jammy, linux/amd64,linux/arm64, yes)	29m 17s
buildx (reference-device, ubuntu:bionic, --build-arg REFERENCE_DEVICE=1 --build-arg BORDER_ROUTIN...	33m 30s
buildx (test, ubuntu:bionic, --build-arg OT_BACKBONE_CI=1 --build-arg REFERENCE_DEVICE=1 --build-...	50m 8s
	3h 8m 18s

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