fix stderr

Author: csmoe

src/test/ui/inference-variable-behind-raw-pointer.stderr

@@ -1,4 +1,4 @@
-warning: type annotations needed
+warning: the type of this value must be known in this context
   --> $DIR/inference-variable-behind-raw-pointer.rs:18:13
    |
 18 |     if data.is_null() {}

src/test/ui/span/issue-42234-unknown-receiver-type.stderr

@@ -1,15 +1,17 @@
 error[E0282]: type annotations needed
   --> $DIR/issue-42234-unknown-receiver-type.rs:17:5
    |
+16 |     let x: Option<_> = None;
+   |         - consider giving `x` a type
 17 |     x.unwrap().method_that_could_exist_on_some_type();
-   |     ^^^^^^^^^^
+   |     ^^^^^^^^^^ cannot infer type for `T`
 
 error[E0282]: type annotations needed
   --> $DIR/issue-42234-unknown-receiver-type.rs:22:5
    |
 22 | /     data.iter() //~ ERROR 22:5: 23:20: type annotations needed
 23 | |         .sum::<_>()
-   | |___________________^
+   | |___________________^ cannot infer type for `_`
 
 error: aborting due to 2 previous errors