fix the wrong fragment name in sampler

Author: FunMelon

openevolve/prompt/sampler.py

@@ -247,7 +247,7 @@ def _format_evolution_history(
 
         for i, program in enumerate(reversed(selected_previous)):
             attempt_number = len(previous_programs) - i
-            changes = program.get("metadata", {}).get("changes", self.template_manager.get_fragment("attempt_no_changes"))
+            changes = program.get("metadata", {}).get("changes", self.template_manager.get_fragment("attempt_unknown_changes"))
 
             # Format performance metrics using safe formatting
             performance_parts = []