Update the rust toolchain to nightly-2024-04-02 (model-checking#3127)

Changes required due to:
- rust-lang/rust@a325bce3cd Normalize the result of Fields::ty_with_args

Resolves: model-checking#3125, model-checking#3113

rust-toolchain.toml

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2024-03-29"
+channel = "nightly-2024-04-02"
 components = ["llvm-tools-preview", "rustc-dev", "rust-src", "rustfmt"]

tests/kani/ValidValues/write_invalid_fixme.rs → tests/kani/ValidValues/write_invalid.rs

@@ -6,9 +6,6 @@
 //! Writing invalid bytes is not UB as long as the incorrect value is not read.
 //! However, we over-approximate for sake of simplicity and performance.
 
-// Note: We're getting an unexpected compilation error because the type returned
-// from StableMIR is `Alias`: https://github.com/model-checking/kani/issues/3113
-
 use std::num::NonZeroU8;
 
 #[kani::proof]