Bump `crypto-bigint` to v0.6.0-rc.5 (#1078) #2021

Job	Run time
build (1.73.0, thumbv7em-none-eabi)	45s
build (1.73.0, wasm32-unknown-unknown)	47s
cross (armv7-unknown-linux-gnueabihf, 1.73.0)	1m 47s
build (stable, thumbv7em-none-eabi)	34s
cross (armv7-unknown-linux-gnueabihf, stable)	1m 40s
build (stable, wasm32-unknown-unknown)	45s
doc	4m 11s
cross (aarch64-unknown-linux-gnu, 1.73.0)	1m 30s
cross (aarch64-unknown-linux-gnu, stable)	1m 25s
test (i686-unknown-linux-gnu, 1.73.0, sudo apt update && sudo apt install gcc-multilib)	1m 41s
cross (powerpc-unknown-linux-gnu, 1.73.0)	1m 44s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	1m 45s
cross (powerpc-unknown-linux-gnu, stable)	1m 23s
test (x86_64-unknown-linux-gnu, 1.73.0)	1m 25s
test (x86_64-unknown-linux-gnu, stable)	1m 22s
	22m 44s

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