submodule: bump third_party/openthread/repo from `79572ec` to `cc8f078` #6594

Job	Run time
buildx (latest, ubuntu:bionic, linux/amd64,linux/arm/v7,linux/arm64, yes)	31m 59s
docker-check	4m 48s
buildx (focal, ubuntu:focal, linux/amd64,linux/arm64, yes)	21m 45s
buildx (jammy, ubuntu:jammy, linux/amd64,linux/arm64, yes)	20m 31s
buildx (reference-device, ubuntu:bionic, --build-arg REFERENCE_DEVICE=1 --build-arg BORDER_ROUTIN...	29m 7s
buildx (test, ubuntu:bionic, --build-arg OT_BACKBONE_CI=1 --build-arg REFERENCE_DEVICE=1 --build-...	31m 58s
	2h 20m 8s

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