Fix debug code challenge (#4632)

tests/challenges/debug_code/data/code.py

@@ -0,0 +1,13 @@
+# mypy: ignore-errors
+from typing import List, Optional
+
+
+def two_sum(nums: List, target: int) -> Optional[List[int]]:
+    seen = {}
+    for i, num in enumerate(nums):
+        typo
+        complement = target - num
+        if complement in seen:
+            return [seen[complement], i]
+        seen[num] = i
+    return None