rustup: update to `nightly-2023-07-08`. #2902

Job	Run time
Lint	3m 31s
cargo-deny	3m 40s
Test (ubuntu-20.04-16core, x86_64-unknown-linux-gnu)	4m 5s
Test (windows-2022-16core, x86_64-pc-windows-msvc)	14m 2s
Test (macOS-latest-xl, x86_64-apple-darwin)	6m 38s
Test (ubuntu-20.04-16core, aarch64-linux-android)	3m 9s
	35m 5s

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