Bump `crypto-bigint` to v0.6.0-rc.5 #638

Job	Run time
build (1.73.0, thumbv7em-none-eabi)	33s
doc	56s
build (1.73.0, wasm32-unknown-unknown)	31s
build (stable, thumbv7em-none-eabi)	31s
build (stable, wasm32-unknown-unknown)	33s
test (i686-unknown-linux-gnu, 1.73.0, sudo apt update && sudo apt install gcc-multilib)	53s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	50s
test (x86_64-unknown-linux-gnu, 1.73.0)	36s
test (x86_64-unknown-linux-gnu, stable)	40s
	6m 3s

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