Fix errors detected by Ruff (#3918)

### What problem does this PR solve?

Fix errors detected by Ruff

### Type of change

- [x] Refactoring

sdk/python/test/test_sdk_api/get_email.py

@@ -1,3 +1,3 @@
 def test_get_email(get_email):
-    print(f"\nEmail account:",flush=True)
+    print("\nEmail account:",flush=True)
     print(f"{get_email}\n",flush=True)

sdk/python/test/test_sdk_api/t_agent.py

@@ -1,4 +1,4 @@
-from ragflow_sdk import RAGFlow,Agent
+from ragflow_sdk import RAGFlow
 from common import HOST_ADDRESS
 import pytest