wasm-builder: Use riscv32emac-unknown-none-polkavm.json target #7221

Job	Run time
preflight / preflight	40s
preflight / ci-versions	56s
test-frame-ui	5m 6s
test-full-crypto-feature	2m 46s
test-node-metrics	15m 26s
cargo-check-benches (master)	21m 10s
cargo-check-each-crate (1)	50m 29s
cargo-check-all-crate-macos	11m 29s
cargo-check-benches (current)	28m 34s
cargo-check-each-crate (2)	46m 28s
cargo-check-each-crate (3)	19m 55s
cargo-check-each-crate (4)	47m 1s
cargo-check-each-crate (5)	59m 45s
cargo-check-each-crate (6)	29m 48s
cargo-check-each-crate (7)	55m 20s
test-frame-examples-compile-to-wasm	3m 1s
test-deterministic-wasm	10m 8s
check-tracing	2m 26s
check-metadata-hash	8m 24s
node-bench-regression-guard	10s
All test misc tests passed	1s
	6h 59m 3s

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