fix tests

Author: estebank

src/test/ui/async-await/async-block-control-flow-static-semantics.stderr

@@ -16,7 +16,7 @@ error[E0308]: mismatched types
 LL | fn return_targets_async_block_not_fn() -> u8 {
    |    ---------------------------------      ^^ expected u8, found ()
    |    |
-   |    this function's body doesn't return
+   |    implicitly returns `()` as its body has no tail or `return` expression
    |
    = note: expected type `u8`
               found type `()`
@@ -57,7 +57,7 @@ error[E0308]: mismatched types
 LL | fn rethrow_targets_async_block_not_fn() -> Result<u8, MyErr> {
    |    ----------------------------------      ^^^^^^^^^^^^^^^^^ expected enum `std::result::Result`, found ()
    |    |
-   |    this function's body doesn't return
+   |    implicitly returns `()` as its body has no tail or `return` expression
    |
    = note: expected type `std::result::Result<u8, MyErr>`
               found type `()`
@@ -68,7 +68,7 @@ error[E0308]: mismatched types
 LL | fn rethrow_targets_async_block_not_async_fn() -> Result<u8, MyErr> {
    |    ----------------------------------------      ^^^^^^^^^^^^^^^^^ expected enum `std::result::Result`, found ()
    |    |
-   |    this function's body doesn't return
+   |    implicitly returns `()` as its body has no tail or `return` expression
    |
    = note: expected type `std::result::Result<u8, MyErr>`
               found type `()`