Update toolchain to nightly-2023-09-19

Propagate changes from rust-lang/rust#115748.

Author: Remi Delmas

kani-compiler/src/kani_middle/reachability.rs

@@ -457,8 +457,8 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MonoItemsFnCollector<'a, 'tcx> {
                 match self.tcx.const_eval_resolve(ParamEnv::reveal_all(), un_eval, None) {
                     // The `monomorphize` call should have evaluated that constant already.
                     Ok(const_val) => const_val,
-                    Err(ErrorHandled::TooGeneric) => span_bug!(
-                        self.body.source_info(location).span,
+                    Err(ErrorHandled::TooGeneric(span)) => span_bug!(
+                        span,
                         "Unexpected polymorphic constant: {:?}",
                         literal
                     ),

rust-toolchain.toml

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2023-09-18"
+channel = "nightly-2023-09-19"
 components = ["llvm-tools-preview", "rustc-dev", "rust-src", "rustfmt"]