sha2: fix RISC-V CI job (#637) #7

Job	Run time
minimal-versions	0s
set-msrv / set-msrv	8s
linux (x86_64-unknown-linux-gnu, 1.81.0)	38s
build (1.81.0, thumbv7em-none-eabi)	28s
linux (x86_64-unknown-linux-gnu, stable)	33s
build (1.81.0, wasm32-unknown-unknown)	18s
macos (1.81.0)	32s
cross (1.81.0, aarch64-unknown-linux-gnu, default)	37s
build (1.81.0, loongarch64-unknown-linux-gnu)	26s
macos (stable)	21s
cross (1.81.0, powerpc-unknown-linux-gnu, default)	38s
build (stable, thumbv7em-none-eabi)	12s
cross (stable, aarch64-unknown-linux-gnu, default)	29s
build (stable, wasm32-unknown-unknown)	35s
windows (x86_64-pc-windows-gnu, 1.81.0)	57s
cross (stable, powerpc-unknown-linux-gnu, default)	31s
build (stable, loongarch64-unknown-linux-gnu)	32s
windows (x86_64-pc-windows-gnu, stable)	2m 12s
	10m 7s

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