fix: test error output and formatting

Author: sassman

tests/ui/attributes/mixed_export_name_and_no_mangle.stderr

@@ -1,17 +1,23 @@
-warning: the attribute `export_name` may not be used in combination with `no_mangle`
-  --> $DIR/E47446.rs:2:1
+error: the attribute `export_name` may not be used in combination with `no_mangle`
+  --> $DIR/mixed_export_name_and_no_mangle.rs:5:1
    |
 LL | #[export_name = "foo"]
    | ^^^^^^^^^^^^^^^^^^^^^^ `export_name` takes precedence
    |
-   = note: when `export_name` is used `no_mangle` is ignored
 note: the `no_mangle` attribute is ignored
-  --> $DIR/E47446.rs:1:1
+  --> $DIR/mixed_export_name_and_no_mangle.rs:4:1
    |
 LL | #[no_mangle]
    | ^^^^^^^^^^^^
-   = note: `#[warn(mixed_export_name_and_no_mangle)]` on by default
+note: the lint level is defined here
+  --> $DIR/mixed_export_name_and_no_mangle.rs:1:9
+   |
+LL | #![deny(mixed_export_name_and_no_mangle)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: remove the `no_mangle` attribute
    |
 LL - #[no_mangle]
    |
+
+error: aborting due to 1 previous error
+