Update Rust toolchain to nightly-2023-12-18 (#2953)

Updates the Rust toolchain to `nightly-2023-12-18`.

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 and MIT licenses.

Author: adpaco-aws

rust-toolchain.toml

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2023-12-16"
+channel = "nightly-2023-12-18"
 components = ["llvm-tools-preview", "rustc-dev", "rust-src", "rustfmt"]