Update Rust toolchain to `nightly-2023-12-18` #5978

Job	Run time
perf	29m 26s
regression (macos-12)	34m 36s
benchcomp-tests	3m 22s
regression (ubuntu-20.04)	19m 55s
bookrunner	15m 45s
write-json-symtab-regression	10m 59s
regression (ubuntu-22.04)	20m 8s
	2h 14m 11s

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