Add test for #24889

Fixes #24889.
r? @Mark-Simulacrum.

src/test/ui/coercion-missing-tail-expected-type.rs

@@ -14,6 +14,10 @@ fn plus_one(x: i32) -> i32 {
     x + 1;
 }
 
+fn foo() -> Result<u8, u64> {
+    Ok(1);
+}
+
 fn main() {
     let x = plus_one(5);
     println!("X = {}", x);

src/test/ui/coercion-missing-tail-expected-type.stderr

@@ -15,5 +15,22 @@ help: consider removing this semicolon:
 14 |     x + 1;
    |          ^
 
+error[E0308]: mismatched types
+  --> $DIR/coercion-missing-tail-expected-type.rs:17:29
+   |
+17 |   fn foo() -> Result<u8, u64> {
+   |  _____________________________^
+18 | |     Ok(1);
+19 | | }
+   | |_^ expected enum `std::result::Result`, found ()
+   |
+   = note: expected type `std::result::Result<u8, u64>`
+              found type `()`
+help: consider removing this semicolon:
+  --> $DIR/coercion-missing-tail-expected-type.rs:18:10
+   |
+18 |     Ok(1);
+   |          ^
+
 error: aborting due to previous error(s)