fix user logs encoding in azure-ai-generative package causing UnicodeEncodeError (#34036)

Author: imatiach-msft

sdk/ai/azure-ai-generative/azure/ai/generative/evaluate/_mlflow_log_collector.py

@@ -30,7 +30,7 @@ def __init__(self, logger):
     def __enter__(self):
         self.logger.debug("Redirecting user output to {0}".format(self.user_log_path))
 
-        self.user_log_fp = open(self.user_log_path, "at+")
+        self.user_log_fp = open(self.user_log_path, "at+", encoding="utf-8")
         self.original_stdout = sys.stdout
         self.original_stderr = sys.stderr
         sys.stdout = OutputCollector(sys.stdout, self.user_log_fp.write)