Set rust-version in Cargo.toml #3

Job	Run time
QEMU build & test (stable, ubuntu-latest, s390x-unknown-linux-gnu, s390x-linux-gnu-gcc)	23s
Clippy	17s
QEMU build & test (stable, ubuntu-latest, i686-unknown-linux-gnu, i686-linux-gnu-gcc)	18s
Build and test (stable, ubuntu-latest, x86_64-unknown-linux-gnu)	14s
Clippy (--no-default-features --features="c-allocator")	25s
Smoke-test fuzzing targets (default)	15s
Build and test (msrv, ubuntu-latest, x86_64-unknown-linux-gnu)	7s
Clippy (--no-default-features --features="rust-allocator")	18s
Smoke-test fuzzing targets (c-allocator)	18s
Build and test (beta, ubuntu-latest, x86_64-unknown-linux-gnu)	13s
Smoke-test fuzzing targets (stable, macos-14, aarch64-apple-darwin)	30s
Build and test (stable, macos-latest, x86_64-apple-darwin)	14s
Smoke-test fuzzing targets (rust-allocator)	19s
Build and test (stable, macos-14, aarch64-apple-darwin)	12s
Miri	41s
wasm32	5s
Build and test (stable-x86_64-gnu, windows-2022, x86_64-pc-windows-gnu)	5s
	4m 54s

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