chore(mkdir): fix assert statement formatting in Windows test

Fix rustfmt formatting violation in test_mkdir_control_characters.
The multi-line assert statement with OR condition was not properly
formatted according to the project's rustfmt configuration.

This resolves a CI formatting check failure.

Author: naoNao89

tests/by-util/test_mkdir.rs

@@ -600,8 +600,10 @@ fn test_mkdir_control_characters() {
         assert!(!at.dir_exists("a/\"\""));
         assert!(!result.succeeded());
         // Check for appropriate error message
-        assert!(result.stderr_str().contains("Invalid argument") || 
-                result.stderr_str().contains("cannot create directory"));
+        assert!(
+            result.stderr_str().contains("Invalid argument")
+                || result.stderr_str().contains("cannot create directory")
+        );
     }
 
     // Test single quotes in path - should work on both Unix and Windows