contracts: fix lowering final declaration without trailing semicolon

Lowering for contract delcarations incorrectly handled the final
declaration statement when it didn't end in a semicolon. This
change fixes the issue.

tests/ui/contracts/requires-block-stmt.rs

@@ -0,0 +1,22 @@
+//@ run-pass
+//@ compile-flags: -Zcontract-checks=yes
+
+#![expect(incomplete_features)]
+#![feature(contracts)]
+extern crate core;
+use core::contracts::requires;
+
+// Compound statements (those using [ExpressionWithBlock]
+// (https://doc.rust-lang.org/beta/reference/expressions.html#railroad-ExpressionWithBlock))
+// like blocks, if-expressions, and loops require no trailing semicolon. This
+// regression test captures the case where the last statement in the contract
+// declarations has no trailing semicolon.
+#[requires(
+    {}
+    true
+)]
+fn foo() {}
+
+fn main() {
+    foo()
+}