Migrate pallet-child-bounties benchmark to v2 #5690

Job	Run time
preflight / preflight	49s
preflight / ci-versions	59s
cargo-check-benches (master)	22m 53s
cargo-check-benches (current)	23m 37s
test-frame-ui	46m 30s
test-full-crypto-feature	2m 42s
test-node-metrics	9m 49s
cargo-check-all-crate-macos	11m 56s
cargo-check-each-crate (1)	22m 30s
cargo-check-each-crate (2)	20m 46s
cargo-check-each-crate (3)	8m 36s
cargo-check-each-crate (4)	20m 40s
cargo-check-each-crate (5)	28m 43s
cargo-check-each-crate (6)	14m 48s
cargo-check-each-crate (7)	31m 24s
test-frame-examples-compile-to-wasm	3m 4s
check-tracing	2m 22s
test-deterministic-wasm	7m 52s
check-metadata-hash	7m 6s
node-bench-regression-guard	14s
All test misc tests passed	1s
	4h 47m 21s

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