dsa: loosen `pkcs8` pre-release dependency (#872) #1522

Job	Run time
test (1.81.0)	16s
build (thumbv7em-none-eabi, 1.81.0)	18s
test (stable)	11s
build (thumbv7em-none-eabi, stable)	11s
build (wasm32-unknown-unknown, 1.81.0)	17s
build (wasm32-unknown-unknown, stable)	14s
	1m 27s

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