Tweak expr.await desugaring Span

Fix #93074

src/test/ui/async-await/proper-span-for-type-error.fixed

@@ -0,0 +1,11 @@
+// edition:2021
+// run-rustfix
+#![allow(dead_code)]
+
+async fn a() {}
+
+async fn foo() -> Result<(), i32> {
+    Ok(a().await) //~ ERROR mismatched types
+}
+
+fn main() {}

src/test/ui/async-await/proper-span-for-type-error.rs

@@ -0,0 +1,11 @@
+// edition:2021
+// run-rustfix
+#![allow(dead_code)]
+
+async fn a() {}
+
+async fn foo() -> Result<(), i32> {
+    a().await //~ ERROR mismatched types
+}
+
+fn main() {}

src/test/ui/async-await/proper-span-for-type-error.stderr

@@ -0,0 +1,16 @@
+error[E0308]: mismatched types
+  --> $DIR/proper-span-for-type-error.rs:8:5
+   |
+LL |     a().await
+   |     ^^^^^^^^^ expected enum `Result`, found `()`
+   |
+   = note:   expected enum `Result<(), i32>`
+           found unit type `()`
+help: try wrapping the expression in `Ok`
+   |
+LL |     Ok(a().await)
+   |     +++         +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.