[BUGFIX] Guard against UnicodeEncodeError when saving validation resu…

…lts in Google Colab environment (ludwig-ai#3875)

ludwig/trainers/trainer.py

@@ -700,7 +700,7 @@ def run_evaluation(
             os.makedirs(dict_save_dir, exist_ok=True)
             dict_save_path = os.path.join(dict_save_dir, f"{progress_tracker.checkpoint_number}.csv")
             llm_eval_examples = pd.DataFrame(llm_eval_examples).to_dict(orient="records")
-            with open(dict_save_path, "w") as outfile:
+            with open(dict_save_path, "w", encoding="utf-8") as outfile:
                 writer = csv.DictWriter(outfile, fieldnames=["inputs", "targets", "outputs"])
                 writer.writeheader()
                 writer.writerows(llm_eval_examples)