p521

Bump `crypto-bigint` to v0.6.0-rc.5 #1005

Job	Run time
benches (stable)	1m 7s
build (1.73.0, thumbv7em-none-eabi)	25s
build (1.73.0, wasm32-unknown-unknown)	22s
build (stable, thumbv7em-none-eabi)	15s
build (stable, wasm32-unknown-unknown)	14s
doc	52s
test (i686-unknown-linux-gnu, 1.73.0, sudo apt update && sudo apt install gcc-multilib)	1m 46s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	1m 37s
test (x86_64-unknown-linux-gnu, 1.73.0)	1m 28s
test (x86_64-unknown-linux-gnu, stable)	1m 22s
	9m 28s

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