Update panic message for missing //@ run-rustfix ui test suite when a .fixed file exists

Author: jieyouxu

Diff for: src/tools/compiletest/src/runtest.rs

@@ -3938,10 +3938,15 @@ impl<'test> TestCx<'test> {
                 self.props.compare_output_lines_by_subset,
             );
         } else if !expected_fixed.is_empty() {
-            panic!(
-                "the `// run-rustfix` directive wasn't found but a `*.fixed` \
-                 file was found"
-            );
+            if self.config.suite == "ui" {
+                panic!(
+                    "the `//@ run-rustfix` directive wasn't found but a `*.fixed` file was found"
+                );
+            } else {
+                panic!(
+                    "the `// run-rustfix` directive wasn't found but a `*.fixed` file was found"
+                );
+            }
         }
 
         if errors > 0 {