Refine the error message. (#5275)

### What problem does this PR solve?

#5265

### Type of change

- [x] Refactoring

agent/component/exesql.py

@@ -52,9 +52,9 @@ class ExeSQLParam(GenerateParam):
         self.check_positive_integer(self.top_n, "Number of records")
         if self.database == "rag_flow":
             if self.host == "ragflow-mysql":
-                raise ValueError("The host is not accessible.")
+                raise ValueError("For the security reason, it dose not support database named rag_flow.")
             if self.password == "infini_rag_flow":
-                raise ValueError("The host is not accessible.")
+                raise ValueError("For the security reason, it dose not support database named rag_flow.")
 
 
 class ExeSQL(Generate, ABC):