[python] add test Missing the important statement for Datetime in Python binding generation (#18175)

* [python] add test on datetime response import

* [python] update sample

* [python] update sample

samples/openapi3/client/petstore/python/test/test_import_test_datetime_api.py

@@ -0,0 +1,38 @@
+# coding: utf-8
+
+"""
+    OpenAPI Petstore
+
+    This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\
+
+    The version of the OpenAPI document: 1.0.0
+    Generated by OpenAPI Generator (https://openapi-generator.tech)
+
+    Do not edit the class manually.
+"""  # noqa: E501
+
+
+import unittest
+
+from petstore_api.api.import_test_datetime_api import ImportTestDatetimeApi
+
+
+class TestImportTestDatetimeApi(unittest.TestCase):
+    """ImportTestDatetimeApi unit test stubs"""
+
+    def setUp(self) -> None:
+        self.api = ImportTestDatetimeApi()
+
+    def tearDown(self) -> None:
+        pass
+
+    def test_import_test_return_datetime(self) -> None:
+        """Test case for import_test_return_datetime
+
+        test date time
+        """
+        pass
+
+
+if __name__ == '__main__':
+    unittest.main()