Fix user agent tag issue

Author: ruiliann666

src/sagemaker/serve/builder/model_builder.py

@@ -528,7 +528,10 @@ def _user_agent_decorator(self, func):
         def wrapper(*args, **kwargs):
             # Call the original function
             result = func(*args, **kwargs)
-            return result + " ModelBuilder"
+            if "ModelBuilder" in result:
+                return result
+            else:
+                return result + " ModelBuilder"
 
         return wrapper