async-signature: bump `signature` to v2.3.0-pre.2 #2307

Job	Run time
build (1.71.0, thumbv7em-none-eabi)	15s
build (1.71.0, wasm32-unknown-unknown)	17s
build (stable, thumbv7em-none-eabi)	13s
build (stable, wasm32-unknown-unknown)	10s
test (1.71.0)	23s
test (stable)	15s
	1m 33s

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