wasm-builder: Use riscv32emac-unknown-none-polkavm.json target #5493

Job	Run time
preflight / preflight	40s
preflight / ci-versions	54s
test-frame-ui	46m 8s
test-full-crypto-feature	2m 32s
cargo-check-benches (master)	20m 50s
test-node-metrics	8m 30s
cargo-check-benches (current)	21m 15s
cargo-check-all-crate-macos	11m 31s
cargo-check-each-crate (1)	18m 6s
cargo-check-each-crate (2)	19m 5s
cargo-check-each-crate (3)	9m 14s
cargo-check-each-crate (4)	16m 37s
cargo-check-each-crate (5)	23m 42s
cargo-check-each-crate (6)	14m 41s
cargo-check-each-crate (7)	31m 8s
test-frame-examples-compile-to-wasm	2m 57s
test-deterministic-wasm	6m 21s
check-tracing	2m 22s
check-metadata-hash	6m 17s
node-bench-regression-guard	12s
All test misc tests passed	1s
	4h 23m 3s

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