fix: adjust the expected error message after rust-lang#132180 was fixed

Author: sassman

tests/ui/attributes/mixed_export_name_and_no_mangle.stderr

@@ -19,18 +19,18 @@ help: remove the `#[no_mangle]` attribute
 LL - #[no_mangle]
    |
 
-warning: the `#[no_mangle]` attribute may not be used in combination with `#[export_name]`
+warning: the `#[unsafe(no_mangle)]` attribute may not be used in combination with `#[export_name]`
   --> $DIR/mixed_export_name_and_no_mangle.rs:11:1
    |
 LL | #[unsafe(no_mangle)]
-   | ^^^^^^^^^^^^^^^^^^^^ `#[no_mangle]` is ignored
+   | ^^^^^^^^^^^^^^^^^^^^ `#[unsafe(no_mangle)]` is ignored
    |
 note: `#[export_name]` takes precedence
   --> $DIR/mixed_export_name_and_no_mangle.rs:13:1
    |
 LL | #[export_name = "baz"]
    | ^^^^^^^^^^^^^^^^^^^^^^
-help: remove the `#[no_mangle]` attribute
+help: remove the `#[unsafe(no_mangle)]` attribute
    |
 LL - #[unsafe(no_mangle)]
    |