fix: get_children should not break supervision tree integrity #668

Job	Run time
docs	3m 8s
Clippy	58s
rustfmt	7s
Run the default tests	2m 54s
benches	3m 51s
Test ractor without async-trait	2m 49s
Test ractor without span propogation	3m 10s
Test ractor with the `cluster` feature	3m 41s
Test ractor with the `blanket_serde` feature	3m 3s
Test ractor_cluster with native async traits	2m 38s
Test ractor_cluster with async_trait	3m 47s
	30m 6s

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