fix: using repr for output patterns

Author: HuanCheng65

grader.py

@@ -337,15 +337,15 @@ def check(
             if not re.search(check["stdout_pattern"], output, re.MULTILINE):
                 return (
                     False,
-                    f"Output does not match pattern {check['stdout_pattern']}",
+                    f"Output does not match pattern {check['stdout_pattern']!r}",
                     None,
                 )
 
         if "stderr_pattern" in check:
             if not re.search(check["stderr_pattern"], error, re.MULTILINE):
                 return (
                     False,
-                    f"Error output does not match pattern {check['stderr_pattern']}",
+                    f"Error output does not match pattern {check['stderr_pattern']!r}",
                     None,
                 )