Upgrade toolchain to nightly-2025-03-07

Changes required due to
- rust-lang/rust#138026: Make CrateItem::body() function return an option

Resolves: model-checking#3930

Author: tautschnig

kani-compiler/src/kani_middle/stubbing/mod.rs

@@ -130,7 +130,7 @@ pub fn validate_stub_const(tcx: TyCtxt, instance: Instance) -> bool {
     let item = CrateItem::try_from(instance).unwrap();
     let internal_instance = rustc_internal::internal(tcx, instance);
     let mut checker = StubConstChecker::new(tcx, internal_instance, item);
-    checker.visit_body(&item.body());
+    checker.visit_body(&item.expect_body());
     checker.is_valid()
 }
 

rust-toolchain.toml

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2025-03-05"
+channel = "nightly-2025-03-07"
 components = ["llvm-tools", "rustc-dev", "rust-src", "rustfmt"]