k256

Update k256 NCC audit link in docs #2238

Job	Run time
benches (1.73.0)	1m 21s
build (1.73.0, thumbv7em-none-eabi)	49s
benches (stable)	1m 11s
build (1.73.0, wasm32-unknown-unknown)	45s
doc	56s
build (stable, thumbv7em-none-eabi)	37s
cross (armv7-unknown-linux-gnueabihf, 1.73.0)	1m 30s
build (stable, wasm32-unknown-unknown)	37s
test (i686-unknown-linux-gnu, 1.73.0, sudo apt update && sudo apt install gcc-multilib)	1m 46s
cross (armv7-unknown-linux-gnueabihf, stable)	1m 12s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	1m 30s
cross (aarch64-unknown-linux-gnu, 1.73.0)	1m 28s
test (x86_64-unknown-linux-gnu, 1.73.0)	1m 30s
cross (aarch64-unknown-linux-gnu, stable)	1m 19s
test (x86_64-unknown-linux-gnu, stable)	1m 16s
cross (powerpc-unknown-linux-gnu, 1.73.0)	1m 26s
cross (powerpc-unknown-linux-gnu, stable)	1m 11s
	20m 24s

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