Bump `rand_core` to v0.10.0-rc-6 (#454) #1045

Job	Run time
build (x86_64-apple-darwin, macos-latest, stable)	1m 17s
no_std (stable, thumbv7em-none-eabi)	2m 2s
build (x86_64-pc-windows-msvc, windows-latest, stable)	1m 43s
no_std (stable, wasm32-unknown-unknown)	1m 52s
no_std (1.85.0, wasm32-unknown-unknown)	1m 51s
test (stable)	3m 40s
build (i686-unknown-linux-gnu, ubuntu-latest, stable, sudo apt update && sudo apt install gcc-mul...	1m 16s
no_std (1.85.0, thumbv7em-none-eabi)	1m 53s
test (1.85.0)	3m 47s
	19m 21s

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