Fix test

src/test/ui/codemap_tests/issue-28308.rs

@@ -10,4 +10,5 @@
 
 fn main() {
     assert!("foo");
+    //~^ ERROR cannot apply unary operator `!`
 }

src/test/ui/codemap_tests/issue-28308.stderr

@@ -3,8 +3,6 @@ error[E0600]: cannot apply unary operator `!` to type `&'static str`
    |
 LL |     assert!("foo");
    |     ^^^^^^^^^^^^^^^
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to previous error