Upgrade rust toolchain to 06-26 (model-checking#3299)

Related change:
- rust-lang/rust@24e41f1d13


Resolves model-checking#3294

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

kani-compiler/src/kani_middle/intrinsics.rs

@@ -77,7 +77,7 @@ impl<'tcx> ModelIntrinsics<'tcx> {
             let Operand::Constant(fn_def) = func else { unreachable!() };
             fn_def.const_ = mirConst::from_value(
                 ConstValue::ZeroSized,
-                tcx.type_of(stub_id).instantiate(tcx, &new_gen_args),
+                tcx.type_of(stub_id).instantiate(tcx, &*new_gen_args),
             );
         } else {
             debug!(?arg_ty, "replace_simd_bitmask failed");

rust-toolchain.toml

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2024-06-25"
+channel = "nightly-2024-06-26"
 components = ["llvm-tools", "rustc-dev", "rust-src", "rustfmt"]