Update type annotations in python_tests

python_tests/artifact/test_backend.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import base64
 import json
 import tempfile

python_tests/artifact/test_backoff.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import io
 import uuid
 

python_tests/artifact/test_boto3.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import io
 from unittest import TestCase
 

python_tests/artifact/test_file_system.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import io
 import tempfile
 from unittest import TestCase

python_tests/artifact/test_prefix.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import io
 import uuid