async-signature: bump `signature` to v2.3.0-pre.2 #973

Job	Run time
build (1.66.0, thumbv7em-none-eabi)	2m 10s
build (1.66.0, wasm32-unknown-unknown)	2m 12s
test (1.66.0)	2m 38s
build (stable, thumbv7em-none-eabi)	11s
test (stable)	35s
build (stable, wasm32-unknown-unknown)	15s
	8m 1s

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