Set rust-toolchain.toml to nightly-2023-12-27 #613

Job	Run time
test (1.70.0, x86_64-pc-windows-msvc, windows-2019)	17m 24s
rustfmt	9s
test (1.70.0, x86_64-pc-windows-gnu, windows-2019, -x86_64-pc-windows-gnu)	20m 53s
test (1.70.0, x86_64-unknown-linux-gnu, ubuntu-latest)	9m 41s
test (1.70.0, x86_64-apple-darwin, macos-latest)	10m 55s
test (stable, x86_64-pc-windows-msvc, windows-2019)	18m 49s
test (stable, x86_64-pc-windows-gnu, windows-2019, -x86_64-pc-windows-gnu)	20m 54s
test (stable, x86_64-unknown-linux-gnu, ubuntu-latest)	8m 57s
test (stable, x86_64-apple-darwin, macos-latest)	10m 57s
test (beta, x86_64-pc-windows-msvc, windows-2019)	18m 22s
test (beta, x86_64-pc-windows-gnu, windows-2019, -x86_64-pc-windows-gnu)	19m 29s
test (beta, x86_64-unknown-linux-gnu, ubuntu-latest)	8m 14s
test (beta, x86_64-apple-darwin, macos-latest)	20m 59s
test (nightly, x86_64-pc-windows-msvc, windows-2019)	17m 58s
test (nightly, x86_64-pc-windows-gnu, windows-2019, -x86_64-pc-windows-gnu)	18m 32s
test (nightly, x86_64-unknown-linux-gnu, ubuntu-latest)	8m 37s
test (nightly, x86_64-apple-darwin, macos-latest)	11m 31s
	4h 2m 21s

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