[integ-test] Fix test_dynamic_file_systems_update_data_loss

The import was mistakenly deleted by aws#6242

Signed-off-by: Hanwen <[email protected]>

tests/integration-tests/tests/update/test_update.py

@@ -15,6 +15,7 @@
 import re
 import time
 from collections import defaultdict
+from datetime import datetime
 
 import boto3
 import pytest