Fix TypeError when summing costs with None values

Filter out None values before summing costs to prevent TypeError.

Co-authored-by: openhands <openhands@all-hands.dev>

simple_data_loader.py

@@ -292,9 +292,11 @@ class SimpleLeaderboardViewer:
                         record[f'{category} score'] = avg_score
                         categories_with_scores += 1
                         if data['costs']:
-                            cat_cost = sum(data['costs'])
-                            record[f'{category} cost'] = cat_cost
-                            total_cost += cat_cost
+                            valid_costs = [c for c in data['costs'] if c is not None]
+                            if valid_costs:
+                                cat_cost = sum(valid_costs)
+                                record[f'{category} cost'] = cat_cost
+                                total_cost += cat_cost
                     else:
                         # Category not submitted - will show as NA
                         pass